The working principle of the solenoid valve, the solenoid valve has a closed cavity, in the different positions of the through-hole, each hole leads to a different oil pipe, the cavity in the middle of the valve, on both sides of the two solenoids, which side of the magnet coils energized valve body will be attracted to which side, through the control of the valve body movement to stall or leakage of different discharge holes, and the inlet holes are always open, the hydraulic oil will be into the different discharge pipes, and then through the oil pressure to push the oil to the different discharge pipes, and then through the oil pressure to push the oil, and then through the oil pressure to the different discharge pipes, and then through the oil pressure to the different discharge pipes. Then through the oil pressure to push the oil just the piston, the piston and drive the piston rod, piston rod drive mechanical device to move. In this way, by controlling the current of the electromagnet to control the mechanical movement.