Oil cylinder or hydraulic cylinder a linear movement actuator which output force is directly proportional to the effective area of piston and the pressure difference on both sides. Its function is to convert hydraulic energy into mechanical energy. Hydraulic cylinder’s inputs include fluid flow and pressure, and the outputs include linear movement speed and force. The piston of hydraulic cylinder can accomplish linear reciprocating motion, and the output linear displacement is limited. Hydraulic cylinder is an energy conversion device used to convert hydraulic energy into mechanical energy for reciprocating linear motion. Hydraulic cylinder is basically composed of cylinder barrel, cylinder head, piston and piston rod, sealing device, buffer device and exhaust device. Buffer device and exhaust device are adopted depending on the specific applications, but the other devices are necessary.