For the doctor's that wear them, we say a "white coat", since it is usually worn over a shirt. It is sometimes referred to as a "lab coat".

oh, when i searched in google it is called " white coat" thanks all of you for your attention.

Hope some native speakers can reply my answer

I am curious if I can call it doctors' white robe .

a doctor's gown http://www.alibaba.com/showroom/doctor%2527s-gown.html