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Aimed at the shortcomings of traditional piston seal of hydraulic cylinder, such as contact seal and gap seal, a combination of contact seal and gap seal in the prior art was proposed to form a new type of tandem combination seal for a hydraulic cylinder. A numerical analysis model of the structure was established, and the flow field pressure distribution, seal deformation and internal leakage characteristics, as well as the influence of structural parameters on the sealing performance were obtained via numerical simulation. The results show that under the same inlet and outlet pressure, compared with the contact seal, the pressure loss in the internal structure of combination seal greater, and the pressure and impact on the seal ring are smaller, which is conducive to reducing the deformation of the seal. The gap seal at the end of the combination seal structure blocks the oil, weakens the oil impact and pressure on the middle seal ring, and thus the seal ring deformation is smaller. The multi-stage sealing structure of combination seal can better shield leakage and improve sealing performance. The leakage in the combination seal is affected by the gap seal length, seal gap and oil pressure, and increasing the gap seal length and reducing the seal gap and oil pressure can reduce the leakage. The internal leakage physical experiments further shows that the proposed combination seal can effectively reduce internal leakage and hence improve sealing performance, and can still restrain or reduce the internal leakage to a great extent and improve the sealing effect and reliability in case of damage failure of the sealing ring. [ABSTRACT FROM AUTHOR]