The riser is a significant device in deepwater drilling operation,and the tension and rigidity are fundamental parameters affecting the safety and stability of the drilling riser.Due to the high cost of introducing foreign riser drilling technology and equipment,the riser tensioning system is independently developed at home.The requirements for the riser tensioning system in offshore drilling were introduced.The composition and working principles of the two tensioners,namely cabletype tensioner and direct cylinder tensioner,were elaborated.The direct cylinder tensioning system was chosen as the design object,some main parameters of the system were designed and calculated,and its rationality was verified,then the relationship curves between tension,rigidity and piston stroke were obtained and analyzed.According to the research findings,the system tension and piston stroke curves are basically the same,but the relationship between rigidity and piston stroke is linear and nonlinear,when the system is working normally;at the same piston stroke position,the tension and rigidity increase with increasing working pressure;under the same working pressure,the larger the piston stroke,the smaller the rigidity of the tensioning system,and the greater the tension.The results obtained ensure the accuracy of system and provide reference for studying the influencing factors of the performance of riser tensioning system.