In this tutorial i will guide you how you can root Huawei P9 Plus after nougat upgrade. This method has been tested on B360 and lower versions of nougat. if you have higher version B37X or B38X, make sure you make full backup in twrp. just in case anything goes wrong, you will be able to restore your phone back to working condition.

Huawei P9 Plus Root Nougat

Supported Models

VIE-L29, VIE-L09, VIE-AL10

Rooting Guide

• You need sd card with 8GB free space (if you want to make full rom backup)
• Backup all important data (rom backup doesn’t include your personal data)
• Enable oem unlock in developer options (tap 7 times on build number to enable developer options)
• Unlock bootloader (How to unlock bootloader?)
• Download root files from THIS LINK
• Extract the downloaded files
• Connect phone in fastboot mode (switch off, then hold volume down and connect with PC)
• Open MAF32.exe file, and type ” fastboot flash recovery  twrpn.img ” then press enter
• If TWRP flashed successfully , type ” fastboot reboot “
• Connect  phone with pc, copy SuperSU zip file in sd card
• Switch off phone and disconnect phone from pc
• Keep holding volume up and power until you see TWRP screen.
• Swipe blue bar on 1st screen to enter TWRP menu
• Tap on install button, and find SuperSU zip file that you have copied to sd card
• Swipe blue bar to install SuperSU
• Once flashed , reboot phone, if you can see superSU app , you have successfully rooted your phone.

Video Tutorial 

Source: XDAforum