Actually if it's only Google Play what you need you can extract the .apk from the .zip and install it manually, but yea, on a JB ROM you have to flash JB Gapps. But first, is important to know what MIUI version you're running, chinese from Miui.com ? JBL ? Or what else. If you have chinese one or JBL build you should have MI-Market in it, so you can download the right Google Play app from it, like hadron already suggested.