Abstract: The state of the art of lockup mechanism is analyzed,and the principle of medical robot is introduced.Based on the friction moment principle of robot joints,the influencing factors of robot joint lockup are described.Main factors influencing the joint lockup performance are determined by experiments and analysis,and the basic relationship between the lockup performance of robot joints and the influencing factors,including piston diameter,cavity diameter,material of friction ring, friction ring average diameter and viscosity of hydraulic oil,is obtained.