Abstract: The balance relationship between bottom hole annulus pressure and formation pressure is a key factor to affect the drilling operation safety. Because of the complex and various situation underground, there is a big error between the actual bottomhole pressure and calculated one. The paper introduced a PWD system which can measure the parameters of weight on bit (WOB), torque, annulus pressure, annulus temperature, pressure inside the drill string, etc., and transmit the measurement data to the ground in real time. With the real time measurement data, the wellbore hydraulic model can be corrected in real time, and the underground situation can be interpreted in real time, what is more, the drilling accident can be predicted in real time. The field test proves the accuracy and reliability of the measurement system. Compared with the storage PWD system, this measurement system is more accurate, and has the function of transmitting the measured data in real time, so it can offer powerful technical support for drilling operation.