Aiming at the problem that the instantaneous rigid force model used for cutting force prediction needs many parameters, and these parameters must be determined in advance through preliminary cutting tests, a new cutting force prediction method without cutting tests was proposed, which could be used to monitor the milling process in actual factories. Based on the bevel cutting model and orthogonal cutting theory, the traditional instantaneous rigid force model was improved to reduce the number of cutting parameters needed for cutting force prediction. In the improved model, only the shear angle parameter was needed which identified from the measured spindle motor torque at the beginning of milling operation, the milling force could be predicted without any extra sensors. In the proposed model, the influence of tool runout was expressed by using the deviation of rotation radius at each cutting edge to accurately predict the cutting force. In order to verify the validity of the model, cutting experiments were carried out. The results show that the predicted value of cutting force is in good agreement with the measured value, in the actual machining process, the machining state can be accurately known without any test milling or any additional force sensor.