How To Root MIUI 9 (Mi Note Marshmallow)

1. First, be sure to have android drivers for your Mi note. You will need it to use fastboot or adb...

• Personally, I use PDANet driver for windows. plug your device and install it, if it fail, restart your computer using "Disable driver signature enforcement" explained here.
• Or use Mi PC Suite

2. Don't forget to have USB Debugging in Developer options (you know how to do it )

3. Next, reboot your phone in fastboot (power +volume down pressed).

• You can also find others mini adb/fastboot like in xda...

4. Now, you have to download the last version of SuperSU, and a special version of TWRP for Mi note :

• Download SuperSU v2.82-SR5 flashable ZIP (or in the official website here (they retiring from supersu - read this)
  
• Download TWRP-3.0.2.0-Virgo (unzip it to get the img file)

5. Put the SuperSu zip in your device (/sdcard/ for example, somewhere accessible with twrp)

6. FINALLY, you have all to root your device !

• I recommend you to put the fastboot/adb mini unzipped in the top of the c: directory, just to be more easier to access, like c:\adb
• put TWRP img next to adb and fastboot file (like in my example in c:\adb)
• Run a command promt :

Code:

cd c:\adb device

List of devices attached

57d7493e

• If you see a number with fastboot like "12345678 fastboot", your smartphone is recognize and in fastboot mode. You can do the next step :

Code:

fastboot boot twrp-virgo.img

7. Your Mi note will reboot with TWRP started (and not installed).

• Touch "Install" and select the SuperSu zip to flash
• Swipe to install...
• For me, it was installed without any error
• BE ATTENTIVE, for any reason, after installing the zip, twrp will you recommend to install their SuperSu, don't do it !! Don't swipe it !!Select the middle button to ignore it, it's an automated function, which is useless and you will need to re-flash your ROM and re root it... (or worst)
• reboot your device
• After reboot, I do not remember but if there is no SuperSu app displayed, just install it from the playstore. Run it. It can ask you to update SuperSu, update it choosing NORMAL mode and Reboot 

8. Your Mi note is rooted !!

Source : miui forum