Purpose: By confirm the change of popliteal arterial position when extension or flexion of the knee and estimate the change of popliteal arterial position after posterior capsular release, we tried to know the position can minimize injury of popliteal artery during arthroscopic surgery and usefulness of posterior capsular release. Materials and Methods: Total of two middle-aged man and woman, fresh frozen cadavers as systemic, all four cases of the knee were included in this study. After the knee was flexed to 0 degrees, 30 degrees, 60 degrees, 90 degrees angle, we estimated distance from posterior tibial cortex to popliteal artery at articular surface, the distal 1 cm and 2 cm from articular surface. We performed posterior capsular release by arthroscopy, and estimated distance between posterior tibial cortex and popliteal artery in the same way. Results: Mean distance between popliteal artery and posterior tibial cortex was 6.3 mm (4.5~7), 4.6 mm (3.6~6), 4.9 mm (3.9~5.8) when knee flexion to 0 degrees at articular surface, distal 1 cm and 2 cm from articular surface each. When knee flexion to 30 degrees, it was 7.4 mm (5.2~9), 4.9 mm (3.6~7.2), 5.3 mm (3.8~6.6). When knee flexion to 60 degrees, it was 8.7 mm (5.4~11), 5.2 mm (4.9~7.3), 6.2 mm (5.4~9.6). When knee flexion to 90 degrees, it was 9.8 mm (5.8~12.1), 5.5 mm (5.1~7.4), 6.5 mm (5.4~10.7). After posterior capsule release, the distance was 6.5 mm (5.5~7.5), 5.8 mm (3.9~7.2), 5.2 mm (3.8~7.0) when knee flexion to 0 degrees, 7.7 mm (5.5~9,1), 7.1 mm (4.6~7.6), 5.5 mm (4.1~6.9) when knee flexion to 30 degrees, 8.9 mm (5.7~11.2), 8.5 mm (5.5~9.2), 6.4 mm (5.3~10.1) when knee flexion to 60 degrees and 10.2 mm (6.3~13.6), 9.5 mm (6.5~11), 6.6 mm (5.9~9.8) when knee flexion to 90 degrees. Conclusion: As knee joint is flexed, the distance from posterial tibial cortex to popliteal artery are increased beween knee joint articular surface and distal 2 cm from knee joint. So popliteal artery injury will be reduced at knee joint surgery. Posterior capsular release could also reduce popliteal artery injury by increasing distance between posterior tibial cortex and popliteal artery.