ABSTRACT Objective：To investigate the clinical effect of tightening and suturing popliteus tendon splithole by Arthroscopy to treatment the lateral meniscus instability in young and middle-aged. Methods：From June 2016 to December2018, 25 patients with unstable lateral meniscus were treatedwith tightening and suturing popliteus tendon splithole in our hospital, including 14males and 11 females, aged 24 to 48 years old. The average age is 36.84±5.53 years. MRI showed: lateral meniscus grade II injury. Arthroscopic exploration: 25 patients with lateral meniscus relaxation, probe hook traction mobility> 11mm. Using All-inside suture technique to close the popliteus tendon splithole, suture the unstable meniscus to the posterolateral capsule, zoom out the popliteus tendon splithole. Compared VAS and KSS scores of patients before surgery with after surgery scores. Results： The postoperative three months follow-up VAS scores ranged from6.76±0.58to 2.60±1.01, P<0.05. The KSS scores ranged from 56.68±4.67to 88.72±3.53, P<0.05. Conclusion： For the lateral unstable meniscus in young and middle-aged, tightening and suturing the lateral meniscus to the lateral joint capsule to zoom out the popliteus tendon splithole ，can enhance the stability of the meniscus.