Objective The finite element models of knee joint before and after mobile-bearing unicompartmental knee arthroplasty (MB-UKA) were established, and the influence from posterior inclinations of tibial prosthesis on contact stress of tibio-femoral joints was studied. Methods Based on computed tomography (CT) and magnetic resonance (MR) images from a healthy subject, the finite element model of healthy knee joint was developed, and the validity of knee joint model before and after MB-UKA was verified. MB-UKA with 7° posterior inclination of tibial component was simulated, and the maximum contact stress of tibial plateau cartilage in lateral compartmen and polyethylene insert was calculated based on joint forces obtained by three-dimensional (3D) motion capture system in MB-UKA model. Results The comparison with results from present literatures showed that calculation results of healthy knee joint model and post-MB-UKA knee joint model were reasonable. The maximum contact stress on polyethylene insert after MB-UKA was greater than that on tibial plateau cartilage in lateral compartment. Conclusions The established finite element models before and after MB-UKA were verified. This study provides a referable method for MB-UKA evaluation.