In production process,the hydraulic station of CNC machine tool does too much useless work,and the heating of hydraulic components is serious,which leads to the short service life of hydraulic components and high failure rate of production.In order to solve this problem,a new type of hollow rotary cylinder with built-in pressure maintaining was designed.The example shows that the oil cylinder can meet the requirements of reducing energy consumption and temperature,and is conducive to improve working environment.It has practical application value.