Abstract: In order to carry out the theoretical research and the structural design of speed control unit for the composite pipeline detector with diameter of 813 mm, a calculation model concerning the deceleration capability of speed control unit was established according to the theory of computational fluid dynamics, and the deceleration capability of the speed control unit under different working conditions was simulated and analyzed, which was verified by the pull test of the composite pipeline detector with diameter of 813 mm. The results show that the designed speed control unit of composite pipeline detector with diameter of 813 mm is capable of reducing the speed at 4.7 m/s as required by the design indicators within the pressure range of (3.4-7.4 MPa) and the flow rate of (8-9 m/s) of medium. Generally, the structural design method of the detector speed control unit combining the simulation analysis based on the theory of computational fluid dynamics and the experimental test is of great guiding significance for improving the structural research, development and design of the detector speed control unit and promoting the progress of the detection technologies of oil and gas pipelines.