Objective To investigate the causes and treatment of gas?related complications during peroral endoscopic myotomy( POEM) for achalasia( AC) . Methods Retrospective analyses were performed on the clinical data of 390 AC patients receiving POEM at Chinese PLA General Hospital from December 2010 to July 2015.Univariate and multivariate analyses were conducted for potential risk factors and treatment for gas?related complications. Results Gas?related complications occurred in 55( 14?10%,55/390) cases. There were 4(1?03%,4/390)cases of pneumothorax, 29(7?44%,29/390)cases of pneumoperitoneum, 23 (5?90%,23/390)subcutaneous emphysema and 7(1?79%,7/390) cardia avulsion during POEM. All gas?related complication were cured by conservative therapy, deflation by puncture or closed drainage of chest cavity.Univariate analysis revealed that tunnel length(χ2=6?209,P=0?045),myotomy depth(χ2=12?354, P=0?002),operation time(χ2=54?905,P=0?000) and previous therapies(χ2=16?920,P=0?000) were risk factors for gas?related complications. Multivariate analysis indicated that previous therapies( OR=4?150, 95%CI:1?875?9?193 ) , tunnel length ( OR=2?410, 95%CI:1?148?5?063 ) , operation time ( OR=4?750, 95%CI: 2?196?10?283 ) were risk factors for gas?related complications for AC during POEM. Conclusion Gas?related complications occurred frequently during POEM, especially for patients with previ? ous therapies of AC. Tunnel length and operative time should be shortened as much as possible. Protective ventilation and CO2 pump should be employed during the whole POEM procedure. Mild complications, pres?ented with merely a small amount of subcutaneous emphysema, do not require any special intervention. If se?vere pneumoperitoneum and pneumothorax occur, puncture should be applied immediately.