Abstract: A study on the contact deformation of a four-stage O-ring sealing structure in an aircraft actuator was conducted using finite element simulation and physical experiments. Based on uniaxial tensile tests of nitrile rubber, the Mooney-Rivlin constitutive model exhibited the highest goodness of fit. This model accurately characterizes the hyperelastic mechanical properties of the material. The mechanical performance of the sealing structure was simulated under low-to-medium pressure conditions. Results revealed that the equivalent stress and equivalent elastic strain of the second-stage seal ring were significantly higher than those of the others. Experimental measurements show that the average contact stress of the second stage seal ring is 3.825 MPa, higher than that of the remaining seal rings. The experimental trends are consistent with the simulation results, confirming that the second stage seal ring acts as the weakest link of the structural system. To mitigate this risk, structural optimization on the inner edge of the piston rod was carried out using the control variable method. The optimization results demonstrate that the equivalent stress reaches its minimum value at a chamfer angle of 20°. Within the allowable range of structural strength, a larger inner fillet radius corresponds to lower equivalent stress. These findings provide a theoretical basis for the reliability oriented design of multi stage sealing systems.