Objective To investigate the effect of arthroscopy debridement and drainage on treating septic arthritis of the knee. Methods Twenty-one cases of acute knee septic arthritis were treated by debridement and synovectomy under arthroscopy and combined with intravenous antibiotics and systematic postoperative rehabilitation. Results The temperature resumed to normal after 3 days of operation. All the knees achieved the normal extension and more than 120 degree of flexion 8 weeks after operation. The clinical results were evaluated through examination of temperature and range of motion of the knee joint. All patients had excellent result. All the cases were followed for 1 to 3 years. No majorcomplications related to the arthroscopy of the knee resulted. According to theNoyes, the rate of excellence and the good was 95.2%. Conclusion Early diagnosis and treatment are mandatory for patients with septic arthritis of the knee. The success of arthroscopy treatment of septic arthritis with diminished morbidity makes arthroscopy an excellent alternative to open surgery.