Abstract: In order to monitor down-hole complex conditions and control bottom-hole pressure,a new drilling method based on micro-flow control has been developed in recent years.As a type of MPD,this technique can identify downhole complex conditions and control the backpressure by adjusting the opening of choke.This technique controls the down-hole pressure accurately by monitoring real time change of drilling fluid’s flow rate in the surface.A Differential Pressure Meter has been developed based on problems of current MFC methods,which can detect the micro-change of downhole flow induced by early kick,lost circulation and other complicated conditions and the information is transmitted to the surface by MWD.Through the borehole experiments for Differential Pressure Meter of the micro-flow,the micro-change of downhole flow can be measured successfully,downhole conditions can be identified in a timely manner with high accuracy.