Predicting the cutting force and accurately computing its dynamic characteristic have great significant for improving the machining accuracy in boring holes on the thin-walled box. It is known that time-varying toolpath and chip breakage are directly affected the boring force in actual machining process. However, majority of the traditional cutting force model commonly fails to consider the influences of tool trajectory and chip fracture, resulting in the dynamic cutting force prediction being almost impossible. In response, an analytical model for estimating cutting force and its dynamic characteristic is deduced utilizing the material properties of maximum shear stress and the law of conservation of energy. Then, a mathematical model describing the relationship between toolpath and cutting force was established considering the effect of the tool motion trajectory. Finally, the predicted model proposed of dynamic cutting force was validated using a field boring experiment under actual boring condition. The results show that the predicted model proposed in this study has good agreement with the experiment. The root mean square value of the dynamic cutting force based on the proposed model was also compared with the classical cutting force model, with a relative error of 4.76%, which verifies the correctness and effectiveness of the proposed model. Overall, this study shows a novel model of predicting dynamic cutting force in the boring process and demonstrates the generating mechanism of dynamic cutting force.