Aiming at the problem of firing accuracy deviation of rapid fire mortar in the state of heeling, the state of the barrel of rapid fire mortar before and after heeling was analyzed by establishing the coordinate system of rapid fire mortar. The mathematical model of firing deviation of rapid firing mortar in the state of heeling was obtained by coordinate transformation. Origin software was used to calculate the direction deviation and distance deviation of rapid-fire mortar at different distances and angles of attack. The results show that the deviation of direction and distance caused by heeling increases with the increase of shooting distance and heeling angle, but the influence on shooting accuracy is different. The deviation of distance is small and can be ignored except for the boundary firing distance, while the deviation of direction is large and should be corrected. The results show that the calculation method and results can provide reference for improving the firing table of rapid-fire mortar.