Objective To analyze stress distribution changes in patellofemoral joints before and after arthroscopic surgery by lateral retinacular release and medial retinaculum placation using three-dimensional (3D) finite element method. Methods The 3D finite element model of pre-and post-operative patellofemoral joints for patients with patellofemoral joint disorders were constructed, and the maximum stress and stress distributions on patellofemoral joints at different flexion angles (30°,60°,90°,120°) under the load of 120 N were calculated and analyzed. Results The maximum stress of patellofemoral joints at different flexion angles after arthroscopic surgery significantly smaller than that before arthroscopic surgery. The stress concentrated on the lateral patellofemoral joints before the surgery, but was redistributed after the surgery. Conclusions The stress on patellofemoral joints at different flexion angles is reduced after arthroscopic surgery by lateral retinacular release and medial retinaculum placation, which provides an objective theoretic reference for arthroscopic surgery to effectively restore stress balance between lateral and medial patellofemoral joints. It is suggested that patients with early patellofemoral joint disorders and abnormal force line should be treated with surgery intervention as early as possible.