Abstract: In this paper, the end-plate speed control pig was taken as an example to investigate the impacts of structure and size of the discharge hole in the speed control pig on the flow field at the discharge hole during the operation of the pig. 4 discharge hole models of same area for speed control pigs were established by using the fluid analysis software Fluent. Then, simulation analysis was conducted on the characteristics of flow field at the discharge holes in the models. It is shown that when the area of discharge holes is the same, the velocity of the gas through the discharge holes with different structures is basically accordant, but the maximum turbulent kinetic energy values after the gas flows through the discharge holes are different. It is proved by the modeling that it is feasible for the prediction of gas flow velocity through the discharge holes to take the limited number of small-area discharge holes to be equivalent to a large area hole. Compared with the discharge holes which are structurally circular or triangular, those of the square structure are better in discharge capacity and lower in turbulent kinetic energy after the gas flows through the discharge hole. Finally, the structure of the discharge hole in pigs was designed according to the simulation results. The industrial application indicates that the model can predict the running speed of speed control pig well, and the relative error is not more than 5.3%. The research results provide the theoretical basis for the design of the discharge holes in end-plate speed control pigs.