Hydraulic cylinder is the executing component in hydraulic transmission system, which is an energy conversion device that converts hydraulic energy into mechanical energy. Hydraulic motors achieve continuous rotary motion, while hydraulic cylinders achieve reciprocating motion. The structural types of hydraulic cylinders include piston cylinders, plunger cylinders, and swing cylinders. Piston cylinders and plunger cylinders achieve reciprocating linear motion, output speed and thrust, while swing cylinders achieve reciprocating swing, output angular velocity (speed) and torque. Hydraulic cylinders can be used not only individually, but also in combination with two or more other mechanisms. To accomplish special functions. Hydraulic cylinders have a simple structure and reliable operation, and have been widely used in hydraulic systems of machine tools.