In order to improve the shooting accuracy of the gun to meet the high quality of the inner surface of the gun barrel, a method of the abrasive water ejection in inner surface machining of gun barrel is proposed. According to the structural characteristics of the barrel with spiral line, used the spiral body abrasive water jet streamer tube, combined with abrasive water jet machining method, the machining device of spiral abrasive water jet design, establish the mathematical model of the abrasive water jet flow numerical analysis and calculation process by using Fluent fluid simulation software. The results show that the method is feasible, and it can provide a reference for abrasive water jet machining the inner surface of the tube body.