Xiomi Mi 3 and Mi 4 use the same fastboot rom file, codename cancro :
NOTICE : flashing any Mi3/4 MIUI V5 rom on Mi 4 LTE will brick it. Mi 4 LTE is supported only by MIUI V6 6.2.1 and later.
That goes for the custom ROMs too, unless stated otherwise.
Operate on the phone. Turn off the phone, press the Volume– key and the Power button at the same time to enter Fastboot mode, then connect the phone to a computer.
Double click on the zip file after downloading is completed to decompile it. Open the folder of the ROM pack, and copy its address on the computer
Decompile and install the ROM flashing tools after downloading is completed (if there’s a security prompt, please select Allow).Open MiFlash.exe and paste the address copied in the last step into the address bar. Click on the first button to Refresh, and MiFlash will automatically recognize the phone. Then click the second button to flash.
Wait until the progress bar on MiFlash is green, which means the ROM is successfully flashed, and the phone will automatically boot.