The seismic response will not only increase the overall oscillation of the transformer-bushing system, but also cause a large top displacement. These factors may cause the fracture of the casing, in order to reasonably reflect the vibration mechanism of the transformer-bushing system under earthquake action and the dynamic interaction between the bushing and the transformer case. Based on the results of the shaking table test and the finite element analysis, by connecting the upper porcelain sleeve to the root flange and the restraining effect of the outer wall stiffness of the box wall on the raised seat as a rotating spring. The simplified model of the three-degree-of-freedom of the transformer-bushing system with the rotating spring is established. The results show that the seismic response of the simplified calculation is basically consistent with the measured data of the shaking table test. verifying the effectiveness of the simplified model. According to the simplified model, the parametric analysis of the rotational stiffness of the two equivalent springs is carried out. the influence of spring stiffness on the casing response is studied, which provides a reference for the preliminary design of the transformer structure.