Abstract: In order to solve the problems including circulation loss,well kick,differential pressure sticking,especially simultaneous kick and loss in narrow density window formation,encountered in the process of conventional drilling related to wellbore pressure,three-parameter automatic pressure control drilling system has been developed on the basis of studying the current technologies at home and abroad.According to the U tube principle,the system gathers drilling parameters including casing pressure,drillpipe pressure and flow rate,etc,and controls these parameters jointly by choke valve automatic control,realizing seamless control shift,the field experiment was carried out in full-scale simulated well.During the control of drillpipe pressure or casing pressure,the entire control process was steady,no overshoot,oscillation and divergence occurred,and pressure control error was no more than 0.2 MPa.In the case of kick and loss of circulation,sensitive flow monitoring and timely control can restrict the volume of overflow and leakage to less than 800 liters total.The test results show the pressure control technique of taking casing pressure,drillpipe pressure and flow rate as control target overcomes the shortage in casing pressure control drilling,offering a better solution for pressure control drilling.