A follow-up device was put forward to reduce the influence of the swing of the gear box on the dynamic balance test of the train wheel set.Due to the existence of the gear box,the dynamic balance test of the train wheel set is not accurate enough.This follow-up device was driven by hydraulic servo,which could limit the transverse swing of the gear box,letting the gear box follow the movement of the main shaft in the dynamic balance test of the wheel set,reducing the effect of swing of the gear box on the dynamic balance test .The mechanical working platform of the follow-up device was designed,at the same time,the hydraulic system was designed and simulated to verify the feasibility of this device.The results show that the hydraulic follow-up device can effectively reduce the effect of gear swing on the wheel set dynamic balance test.