Unlocking Bootloader will delete all data on your SD card. Make sure you have saved all your data in this step.
Shut down your phone and hold down VOLUME UP and POWER for about 5 seconds. Then the screen will get into the interface of bootloader.
Starting to install the drivers
Connect your phone to the computer with a USB cable. Right click "My Computer", select "Manage" and then select "Device Manager", right click the unrecognized "Android 1.0" device, and then select "Update Driver". Choose to manually install the driver, select miui_ns/drivers/x86 directory (users of 64-bit system select miui_ns/drivers/x64), and then always click Next to complete the installation. During this process, you may be asked to choose whether to continue the installation, select Yes. After successful installation, the system can identify your phone as Android Phone.
Please note that if the text on the bootloader interface is "LOCK STATE - UNLOCKED", it means your phone is already unlocked, you may skip the following steps and go directly to the second section to flash Recovery; if the text is "LOCK STATE - LOCKED", please continue to the next step.
Double click unlock.bat in the directory of miui_ns / fastboot on the computer (if your computer does not display the file extension, double click the unlock file).
The unlock prompt interface will appear on your phone, as shown in the following picture on the left, press VOLUME to select YES, and then press POWER to confirm. Well, bootloader has been unlocked now.
You will see the unlocked bootloader screen as shown in the following picture on the right, stay here.