In the hydraulic braking system of railway transportation industry,to control the braking force,the Pulse Width Modulation（PWM） is usually used to adjust the pressure of the electro proportion valve.In some special condition,there are noise and vibration from the electro proportion valve.The current of the electro proportion valve has a high amplitude displayed in the oscilloscope,and the displacement of the core has a high amplitude too,which lead to the noise of the electro proportion valve.By increasing the frequency of the PWM signal or improving the inductance of the electric circle,the amplitude of the current and the displacement of the core could be reduced effectively.Finally,the abnormal noise of the electro proportion valve was eliminated effectively by experiment.