In view of the phenomenon that the large vibration of the car body floor leads to uncomfortable riding under the original hanging stiffness of a certain type of EMU, the optimal design of the hanging stiffness of traction transformer of the EMU was carried out. In the process of optimization design, the Latin hypercube design (LHD) method was used to sample. According to the sample data obtained, the adaptive response surface method (ARSM) was introduced to optimize the design of the suspension stiffness of transformer, which avoided the problem that the traditional response surface method was completely dependent on the original sample points. After the design optimization, the hanging stiffness of traction transformer was verified, and it was found that the vertical vibration acceleration of the car body floor was greatly reduced. The hoisting frequency was 9.0 Hz, which was much lower than the first vertical bending frequency of the rigid hanging car body. After modal analysis, the first vertical bending frequency was kept above 10 Hz, which conformed to the requirements of the modal matching for EMU.