Abstract: Back-pressure compensation system in managed pressure drilling can be characterized by high cost and a large occupied drilling field site.Under such circumstances,an automatic diverting manifold system has been developed to replace the existing system.With its simple structure and high adaptability,the innovative automatic diverter manifold with different operation modes of single drilling pump,with dual pumps and large flow rates in conventional drilling operations which can satisfy the demands of different operation mode shifts in finely managed pressure drilling.A mathematical flow model for the innovative automatic diverter manifold system has been established based on mass conservation,momentum conservation and control over throttle valves,and the numerical flow method is used to solve the mathematical flow model.Both the fluid flow calculation results and computational fluid dynamics simulation results show that this automatic manifold system can control wellhead pressure within set pressure and meet the needs of fine pressure control drilling.