0bjective To analyze therapeutic effect of posterior ankle arthroscopic treatment of the Flexor Hallucis Longus Lesion in Posterior Ankle Impingement Patients． Methods From October 2018 to December 2019, Clinical records of 20 patients with symptomatic Os trigonum or Stieda process with Flexor Hallucis Longus Tendon lesion removed by ankle arthroscopy were reviewed．All of them showed pain in the posteromedial ankle joint, and the pain was aggravated with active and passive plantar flexion.There were 13 males and 7 females with an average age of15-40 (24.1±7.1) years.The preoperative and postoperative Visual Analogue Scale（VAS）score, American Orthopaedic Foot and Ankle Society (AOFAS) Ankle-Hindfoot Score were followed up and compared. Results All patients were followed up for an average of 15~30（23.2±4.3）months．The average of AOFAS was 94.4±2.3 after operation．while it was 68.1±4.0 before operation(t=27.40，P<0.001)．The score of VAS after operation(1.00±0.65)was significantly lower than that before operation(7.25士0.72)(t=28.92，P<0.001)． Conclusions Posterior ankle arthroscopic repair of the Flexor Hallucis Longus Tendon Lesion in Posterior Ankle Impingement is effective and the pain and the joint function were improved significantly.