Combined seals, as a kind of reciprocating seals, are widely used in the hydraulic systems. One combined seal usually contains two or more elements to achieve the sealing function. Not only the interference fit between the seal and the rod/groove should be considered, but the assembling parameters between the inner sealing elements are also essential to be investigated. Stretching ratio, as one indicator for the interference fit, usually exerts a significant influence on the sealing performance. However, in the study of stretching effects on combined seals, the traditional axisymmetric modeling method would introduce the over-stretching problems, resulting in large errors. To overcome the above problem, this paper proposed a putter-movement method, where an extra putter is introduced into the model, and mixed lubrication theory was employed to study the macro and micro characteristics among the sealing zone. As a typical kind of combined seals, the VL seal was utilized as the research object, and the material's plastic effects are included in the reciprocating-seal modeling for the first time. The numerical results were compared with the experimental data, and good agreements were obtained. The proposed method was then employed to systematically discuss the sealing characteristics under different interference-fit conditions. The results indicate that the stretching mainly affects the contact pressure on the cavity side. Compared to the performance of the standard geometry, with extra-stretching, the leakage is increased, but the friction is decreased.