When grinding car is in the process of work, the grinding motor adjusts its grinding angle by deflection hydraulic cylinder, and severe vibration will appear when the cylinder is working. In order to study the vibration characteristics, firstly, the working principle of the hydraulic system of the grinding motor was analyzed, then the mathematical model of the force of the hydraulic system was established and the AMESim hydraulic simulation software was used for simulation. Results showed that, when there was hydraulic-lock, the hydraulic cylinder speed was stably when the cradle deflection angle was within 20 degrees; when the deflection angle was greater than 20 degrees, the cradle started vibrate, the amplitude and frequency was greater with the increase of deflection angle. In order to solve this problem, a method for adding throttle valve or overflow valve was proposed.