Objective To investigate the changes of masseter muscle after mandibular angle osteotomy.Methods A total of 26 patients were treated with mandibular angle osteotomy from July 2009 to June 2015.Three-dimensional reconstruction by maxillofacial CT was used to measure the maximum cross-sectional area of masseter muscle before operation,10 days and 1 year after operation.Meanwhile,the masticatory efficiency was measured and the variance analysis was performed.Results The maximum cross-sectional area of masseter muscle increased 10 days after operation (P＜0.05).Compared with the pre-operation,the maximum cross-sectional area decreased slightly 1 year after operation,and there was no significant difference between the 2 groups (P＞0.05).The masticatory efficiency decreased significantly 10 days after operation (P＜0.05).Compared with the 10 days post-operation,the masticatory efficiency increased significantly 1 year after operation (P＜0.05).And there was no significant difference of masticatory efficiency between 1 year post-operation and preoperation (P＞0.05).Conclusion The masseter muscle function can be restored 1 year after mandibular angle osteotomy.