The dynamics coupling problem for the self designed “3 parallels∪2 series” mixed type NC machine tool was studied based on the kinematics and force rule of mechanism in order to ensure that the machine can have good dynamics characteristics and high quality of parts during the process of machining complex surface. A method based on Kane and Lagrange was put forward. A whole dynamics coupling model of serial and parallel mechanism was established and the coupling factors were determined. The process of machining complex part and the force of machine tool were dynamically simulated. The simulation results showed that the established dynamics model was credible and reliable, and in accordance with dynamics rules of the force and kinematics relations. The experiment was made to cut complex surface parts and the machine tool run smoothly with fast speed. There was no large singular position and coupling error. The surface roughness results showed the kinematics accuracy of the machine tool and interference fringe proved the force uniform of machine tool. As there was no singular coupled vibration and collision, it was proved that the theoretical analysis was correct. The method and process can solve dynamics coupling problem actively, real-timely and effectively of 3PTT-2R NC machine tool, and lay a foundation for accurate control of NC machine tools.