The dynamic analysis of a gear transmission system for electric vehicle is analyzed by means of a multibody approach. The architecture of the transmission is constituted of one gear ratio, with the differential integrated in the same gear box. The multibody model of the complete transmission has been created and optimized in order to get the dynamic response of the system. In particular, the frequency response function of the system in terms of rotational speed and loading forces has been determined. Furthermore, the dynamic transmission error has also been determined.