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 medium-low pressure conditions. Results revealed that the equivalent stress and equivalent elastic deformation of the second-stage seal ring were significantly higher than those of the others. Experimental measurements showed an average contact stress of 3.725 MPa for the second-stage ring. This represents a 22.1% increase compared to the first stage. These experimental trends are consistent with the simulation results, confirming that the second-stage seal is the weakest link in the structural system. To mitigate this risk, structural optimization of the piston rod's inner edge was performed using the control variable method. Optimization results indicated that the contact stress is minimized at a lead-in angle of 20°. Furthermore, a larger inner fillet radius leads to lower contact stress, provided it remains within the allowable limits of structural strength. These findings provide a theoretical basis for the reliable design of multi-stage sealing systems.