By using the response surface methodology, high-speed milling expeeiments of P20 mold steel were performed. The forecasting model on relationship between the milling force and cutting parameters of milling speed, feed amount of each tooth, cutting depths in radial and axial directions was established, and the significance of the model was tested. Moreover by comparing the predicted results of the model with the measured dates, the accuracy of the model was verified. The influence law of the milling parameters to the milling force is obtained by analyzing the response surface and its contour lines.