Abstract: According to the characteristics of the existing serial elastic dynamic vibration model of three masses and three degrees of freedom for a gantry crane with elastic trolley frame, the numerical solutions to the dynamic behaviors of the system are obtained through modal analysis. The coupling relationship and variation law between the structural parameters and dynamic indexes of the gantry crane is emphatically studied. It reveals that the rail gauge of the trolley has a big effect on the natural frequency of the system; however, the stiffness coefficients of the girder and the trolley frame have little effects on the dynamic factor of the system.