Original: https://nvidiashieldzone.com/the-nvidia-shield-portable/shield-tablet-root/root-shield-portable-lollipop-5-1/
Attach a flash tutorial: https://blog.csdn.net/qq_21153225/article/details/86013335
Advance preparation:
Smallest ADB and Fastboot (60129 Downloads) (official page) Shield Family Drivers (7224 downloads) (original page) TWRP (Shield Portable Version) (3554 downloads) (Original page) TWS SuperSU (6186 downloads) (updated version possible here)
Note 1: The unlocking boot loader wipes everything internally (not on the external SD card if it exists). Make sure everything is saved and backed up. You must exit Google – so be sure to have the Google Authenticator application ready if you use two-step authentication.
The installation
 

if not already installed, install minimum ADB and Fastboot. Be sure to extract the Shield family of drivers somewhere in the system and determine their location. Make sure you know how to access the Device manager on your PC. Place the TWRP recovery image in the Minimal ADB and Fastboot folders (usually c: \ program files (x86) \ Minimal ADB and Fastboot \). Name it something you will remember. Copy supersu.zip to the Minimal ADB and Fastboot folders and use a USB cable to plug the Shield Portable into the PC. Verify that the DRIVER for ADB is installed:
on PC, go to device manager. Find yellow (!) The ADB device. If not, you probably already have a driver. Skip to step preparation step 8. Right-click the device and select Update Driver. When provided, browse the computer to find the driver and point it to the Shield Family Drivers folder that you extracted in step 2 above. After completing the driver installation, (!) Yellow devices should disappear.

enables developer mode on Shield Portable.

on Shield Portable, go to setup – > About – & gt; BUILD (click 7 times on BUILD to unlock developer mode)

enables USB debugging on Shield Portable

setting – > Developer – & GT; Debugging; If set to open, a pop-up window should appear requesting authorization for the PC. Select the No Longer Ask this PC box and select Allow. If it doesn’t show now, it will show later.

Start step

restart Bootloader on Shield
starts minimum ADB and Fastboot from the start menu or icon on your PC. This will get you into a black DOS box. Type “Adb Devices” and make sure the Shield Portable appears. Note: If you did not have a pop-up window on the Shield Portable screen in Step 9.2 above, it might appear now. You must authorize the PC before it appears on the ADB device. Once you see your Shield Portable listing when you run adb Devices, you can proceed. Type “ADB Reboot Bootloader” and press Enter. Shield Portable should be restarted to the boot loader screen.

to verify whether the Fastboot driver has been installed:

on PC, go to device manager. Check to see if there is a yellow (!) that mentions FASTBOOT. . If not, proceed to root process step 3.1. When you right-click on the device and select Update Driver offer, browse the computer to find the driver and point it to the Shield Family Drivers folder that you extracted in step 2 above. After completing the driver installation, (!) Yellow devices should disappear. Type “Fastboot Devices” and make sure your Shield Portable is visible.

unlock Bootloader (if your Bootloader is unlocked, go to step 5 of the Root procedure.

type ‘fastboot OEM unlock’ and press Enter. You’ll see a sign on the Shield Portable screen, please wait… This will take a few minutes. Don’t be impatient! Let it be done.

restart to the Shield portable interface

unlock the boot loader, restart Shield Portable and return to the Shield Portable main interface.

repeat the above preparation steps 8 and 9 to re-enable developer/USB debugging. Note: At some point, you will have to reauthorize your PC; Be sure to check the Shield Portable screen for an authorization prompt if the ADB command fails. Push supersu.zip to the device

in the Minimal ADB and Fastboot DOS Windows, type: “ADB push supersu.zip/sdcard/” and you should see the text indicating that the file has been copied correctly.

restart to Bootloader

type “adb reboot bootloader” and press Enter. Shield Portable should be restarted to the boot loader screen.

Fastboot Boot TWRP

enter “fastboot devices” and make sure your Shield Portable is visible. If the Shield Portable is listed, type “Fastboot Boot TWRP-3.0.2-0-Roth. Img” (or anything you name) and press Enter. This temporarily introduces the Shield Portable into TWRP. It cannot replace recovery. You should see the TWRP restore screen

install SuperSU

select install. Navigate and select Supersu.zip. Follow the instructions and slide to FlashSuperSU to install.

restart to the system

select REBOOT from the TWRP menu and then select SYSTEM. If you ask any questions about repairing or restoring ROOT, please answer no

connect to the computer, use the brush wizard, swipe recovery, select twrp-3.0.2-0-roth. Img, and then swipe into the SYSTEM to restart the device and run SuperSU application
After the ol> backup is up and running (it may take longer to get started for the first time), find the SuperSU application installed on Shield Portable. Run it and perform any upgrades (select “Use normal” if required). After downloading, select continue, restart

and root is finished!

Video tutorial
[YouTube id = “vyOoOPXhPlg” align = “center” maxwidth = “600”]
If things go wrong
First, don’t panic. It would be difficult to “plug” the Shield Portable permanently by trying root.
Whatever the problem, the flash of a stock image should get you back to work.
Follow our tutorial: Restore to stock picture instructions
Access Bootloader by hardware

ensure that the equipment is turned off. (If stuck on some screens, hold the shield button until the device is off). Hold HOME + BACK and click the Shield button. Shield should start to Fastboot/Bootloader (you can also enter Recovery from there).