Abstract: How to safely run the casing to the predetermined position is one of the technical challenges in completion of structurally-complex wells such as extended-reach wells, branch wells and cluster wells. A circulating pushing casing running system (with mud circulation and pushing forces) was developed. The system can automatically connect casing, establish drilling fluid circulation, rotate the casing string and generate axial oscillation force at the end of the casing string to reduce casing running friction. Moreover, it is capable of removing sand bridges and steps by cutting the borehole wall. This paper introduces the structure and working principles of the key devices of the system, namely the casing circulating rotating device and casing pushing running device. Numerical simulation and laboratory testing were performed to analyze the slip load-bearing capacity of the casing circulating rotating device. The results show that the casing circulating rotating device works reliably, and can bear an axial load of 2400 kN, a torque of 30 kN · m and sealing pressure of 35 MPa. Under the designed pump rate, the pressure drop through the casing pushing running device is 2.7 MPa, and the oscillation force is 41 kN. Field testing shows that the circulating pushing casing running system effectively improves the safety of casing running.