As a connection device in underwater production systems, the sealing performance of subsea connectors directly affects the feasibility of deep-sea oil and gas field development. To address the issue of inherent machining errors affecting sealing reliability, this study takes the subsea horizontal clamp connector and its metal lens-type sealing ring as the research object. It analyzes the influence of geometric variations in the sealing ring caused by machining errors on sealing performance. The research first clarified the correlation between the contact stress of the sealing ring and relevant structural dimensions through mechanical analysis. Subsequently, three relevant structural dimension parameters were selected. Using Latin Hypercube Sampling, sample datasets were generated within their actual machining error ranges. Finite element analysis (FEA) was then employed to obtain the corresponding sample set of maximum contact stress in the sealing zone. Based on the FEA results, a multiple linear regression model relating contact stress to the dimensional parameters was constructed. Based on the assumption that dimensional errors follow a normal distribution, Monte Carlo method was applied for reliability analysis, yielding a calculated sealing failure probability of 0.024. Sensitivity analysis revealed that the outer ring length and spherical diameter of the sealing ring have the most significant impact on sealing reliability.