There are two main ways that you can take a screenshot on Xiaomi MIUI 6
Press both the Power Button and Volume Down Button simultaneously for about 1.5 seconds.
Go to notification panel then swipe up. You’ll see the Screen Capture toggle there.
Xiaomi MIUI 6 review
Xiaomi MIUI 6, the latest version of its popular xiaomi’s custom Android UI, bringing a design change that will have more than a few people thinking of iOS 7.