In the process of actual wheelset assembly, in order to eliminate the influence of a series of factors on the accuracy of the cylinder force dispalyed, making sure the cylinder pressure value is accurate. The error of the cylinder pressure displayed in the interface of control software was analyzed in detail. The method of quadratic curve fitting and its practical application in pressure calibration were introduced. The pressure error values of cylinder pressure before and after calibration were compared. The results show that the validity of the application of quadratic curve fitting method in pressure calibration of cylinder is effectively improved. 