In this paper, focusing on the coupled vibration of light weight vehicle engine and frame, the efficient method to reduce the vibration is discussed. First, target coupling vibration is explained by experimental data. And transfer force identification which transmits from the engine to the frame through the engine mount is carried out using dynamic stiffness method. In order to explain how the engine and the frame are coupling, the coupling index is introduced. The index is defined by inner products of the identified force and the frame FRF. Finally, the method to reduce the coupling index by adjusting the engine mount angle is proposed. The optimal adjustment angle is predicted and modifying the angle in experiment, it is shown that the adjustment method can reduce the coupling index and coupled vibration.