Soft start-up valve is used to input compressed air into pneumatic system slowly and has the effect of safety and protection. Air intake is connected with the input P of Soft start-up valve. If coil is energized, the 3/2 way valve opens. At this time, a little air comes to output A through throttle valve, which increases the pressure of the system gradually; when the output pressure is equal the half of the input pressure, Soft start-upvalve completely opens and the flow at this time reaches the highest value of itself. When the coil is de-energized, air intake P closes, the air returns to R orifice through reflux valve and is quickly exhausted. The pressure of the system falls to zero, which protects the whole system.