In the hydraulic cylinder,the surface contact stress of reciprocating dynamic seals is the key to determine the sealing effectiveness.However,due to great difficulty in monitoring surface contact state of reciprocating seals in the working process,the change rule of contact stress of sealing structure still remains less understood.Taking the Y-ring in hydraulic cylinder as the research object,the influence of inner lip wear of Y-ring on the surface contact stress of sealing groove was analyzed and the best stress monitoring points were located based on finite element simulation.Fiber bragg grating (FBG) was applied to monitor the contact stress on outer surface of the sealing groove.Data acquired from FBG sensors laid in the sealing groove shows that with the increase of wear degree of the inner sealing lip,the radial and axial contact stresses first increase and then decrease,which is consistent with the simulation results.The response sensitivity of contact stress to the seal wear degree increases with the increase of seal pressure.This study provides basis for the condition monitoring of Y-ring in the service process of hydraulic cylinder.