A brief introduction to the function of the tensioner in offshore drilling and the current research situation in China were made. The operation modes of the compensation system and the tension modes of the cable-type tensioner and direct action tensioner(DAT)were expounded. Through comparing the advantages and disadvantages, the passive DAT system was chosen as the design scheme. The DAT system’s structural components and design principles were described in detail. The important component hydraulic cylinder was designed. Based on the 3D model built with UG, parts of systems were conducted with static analysis using ANSYS Workbench. Through checking the dangerous positions and optimization, it was proved that the design was reasonable.Finally, hydraulic cylinders’vibration natural frequency was gotten through conducting modal analysis. Hydraulic cylinders would not appear resonance phenomenon. Therefore the system’s reliability is ensured and technical support is provided for hydraulic system’s design.