I want to do a serial communication Raspberrypi and voice recognition module v3, and for that I have to disable the system used UART port raspberrypi3. After disabling the raspberrypi3 b+ system used UART pot can we able to communicate with inbuilt Bluetooth as before at the same time?
Yes you can use Bluetooth and a UART at the same time on the Pi3B.
The full UART is used to talk to the Bluetooth module on the Pi3B. That still leaves the mini UART available. Fortunately the mini UART uses the same GPIO/pins (as the full UART).
In particular see
and if you are interested in the detail