Abstract: Piston rings are the most widely used sealing elements in aero-engine accessory sealing systems. Pressure differential and backpressure are the primary operating parameters governing their sealing performance. To reveal the influence law of pressure difference and backpressure on the sealing performance of piston ring, this study employed a sealing test system for coordinated regulation of pressure difference and backpressure to investigate the variation laws of leakage rate and equivalent flow area (A_Cd) under various pressure difference (0.02, 0.04, 0.06, and 0.08 MPa) and backpressure (0.1, 0.2, 0.3, and 0.4 MPa) working conditions. The results indicate that the leakage rate of piston ring varies markedly with inlet pressure difference and outlet backpressure, and rising pressure difference and backpressure both result in greater leakage. At constant backpressure, A_Cd decreases as pressure difference increases; conversely, at constant pressure difference, A_Cd increases with increasing backpressure. In summary, backpressure, together with pressure difference, constitutes key operating parameters affecting piston ring sealing performance. Accordingly, piston ring design should consider the combined influence of both parameters to ensure reliable sealing performance under various operating conditions.