Abstract: In order to monitor down-hole complex conditions,a new micro-flow rate measurement device,based on the structure of stabilizer and choke pressure difference theory,had been developed.It monitors the micro-flow rate changes of drilling fluid from inside drill pipe to annulus space accurately,and transmitts the data or information to the surface by MWD,improving the ability of monitoring complicated downhole conditions,and realizing real time monitoring of overflow.This article introduced the theoretical model of micro-flow rate nipple,derived mathematical formulas of flow rate change and pressure difference when oil and gas kicking,used ANSYS to simulate different working conditions,analyzed and compared theoretical calculation result with experimental data collected in the field.The field test showed that the device ran stablely for a long time,and endured every kind of trial in different conditions,the actual sensitivity had reached 0.5 L/s,with obvious superiority for monitoring bottomhole kicks,especially for gas kick.