Objective To investigate the correlation between skeletal muscle density SMD of L radiotherapy and prognosis of esophageal squamous cell carcinoma ESCC . Method This study was a 3 re v t e r r o t s e p b e r c a tiv b e efo c r a e se and after study of patients diagnosed with esophageal squamous cell carcinoma between March 2012 and November 2018. The skeletal muscle density of L3 cone skeletal muscle area of L3 cone subcutaneous fat area of L3 cone and visceral fat area of L3 cone were measured before and after radiotherapy. Hazard ratios were used to assess the association between changes in SMD and overall survival OS before and after radiotherapy. Kaplan-Meier curve and Cox proportional risk model were used for survival analysis. Result Among 258 patients with esophageal squamous cell carcinoma 162 patients in the L3 pyramidal subcutaneous skeletal muscle density increase group after radiotherapy were followed for a median of 22. 4 months ranging from 3. 3 to 92. 4 months . Through univariate Cox proportional risk analysis we found that changes in SMD age ≥60 years and tumor length after radiotherapy were independent prognostic factors affecting overall survival P< 0. 05 . Conclusion Changes in subcutaneous skeletal muscle density before and after radiotherapy can be used as a prognostic biomarker for overall survival in ESCC patients.