Abstract: The production efficiency of involute spline broaching tool is limited due to the need of multiple grinding to ensure the preparation accuracy of subsequent spline holes. In order to solve this problem, it is necessary to study the determination method of the optimal correction tooth profile of involute spline broaching tool with a pair of back angles. In this paper, the involute replacement theory is used to correct the tooth profile and the least square method and numerical search method are combined to solve the alternative involute function. In the case analysis, the optimal pressure Angle is controlled to 0.01°, and the minimum of tooth profile error is obtained. In the same group of error points, the total error of tooth profile fitting by the substitute involute method is 0.001 mm better than that by the substitute circular arc method. The cross-bar distance error of the broach is less than 0.01 mm. The 5 level precision of the involute internal spline gear is tested by matching P26C tooth profile.