Abstract: A numerical analysis model for predicting the performance of a hydraulic reciprocating Glyd-ring seal based on soft EHL theory was developed, which consisted of fluid mechanics, contact mechanics, deformation analysis and thermal analysis. The film thickness distribution, fluid pressure and contact pressure distributions, as well as fluid transport per stroke and friction force on rod were performed to reveal the mechanism of hydraulic Glyd-ring seal. In addition, the influences of root mean square (RMS) roughness, sealed pressure and rod speed on sealing performance of such seal were analyzed. Analysis results indicate that the seal was under mixed lubrication, and the sealing zone was primarily contact by the contacting asperities of seal surface in this study. Furthermore, a relatively small RMS roughness had better sealing performance. And an increased sealed pressure resulted in an increasing in leakage and friction force on the rod, while an increased rod speed was propitious to reduce the leakage.