Aiming at the interface reconstruction problem of O-rings under different working conditions in aircraft landing gear buffers, this study establishes a high-precision finite element calculation model to investigate the effects of pre-compression ratio and oil pressure on the stress distribution of the O-ring. Based on the Mooney-Rivlin hyperelastic constitutive model, the finite element simulation combined with the boundary condition update method is adopted to construct a dynamic contact interface model of the O-ring, revealing the evolution rule of the Von-Mises stress under different compression ratios (10%–25%) and sealing pressures (5–20 MPa). The results indicate that during the pre-compression phase, both the maximum Von-Mises stress and contact stress increase significantly with the increase of the compression ratio. Under the oil pressure, the stress peak shifts from the middle of the O-ring to the gap of the guide sleeve, thereby increasing the risk of biting and highlighting the necessity of optimizing the gap and chamfer design. Furthermore, the contact stress exhibits asymmetric distribution under the influence of the sealing pressure. The modeling method and simulation results proposed in this study provide a theoretical foundation for the design and life evaluation of the aircraft sealing structure and emphasize the critical importance of optimizing the geometric parameters of the guide sleeve in restraining seal failure.