The study object was hydraulic spool valve in oil supply system for an aircraft,the relationship between the friction of the spool and jet force to the hydraulic spool valve stuck was researched.The motion function of the spool was established,including the hydraulic radial force model,the jet force model and the friction model between the spool and sleeve.The whole spool system model was constructed by using AMESim,and sticking problem was reappeared by simulation analysis.The results indicate that the excessive friction is the reason of the spool stuck.The friction is generated when the spring makes the spool contact with the sleeve,because the spool is affected by acceleration.The reliability analysis flow of the spool was proposed.Considering the randomness of structural dimension parameters of the spring,the reliability of the spool valve was calculated by using Monte-Carlo method,and the parameters were optimized.The results indicate that major impact factors about the reliability were e1 and e2 ,which were the limit deviations of the spring.And e2 is the most sensitive of them.Through the parameter optimization,the parameters applicable range of the spool no stuck are obtained.And the analysis flow provides reference to the selection of spring in the spool.