Objective To explore the changes of masseter muscle function after mandibular angle osteotomy through electromyography analysis. Methods From October 2010 to June 2015, 18 patients who received mandibular angle osteotomy were selected. The masseter electromyogram was analyzed before operation, one month and one year after operation. The difference was statistically analyzed. Results Compared with the masseter electromyogram before operation, the masseter electromyogram one month after operation was significantly decreased (P<0.05). While there was no significant difference between the masseter electromyogram one year after operation and that before operation (P>0.05). Conclusion The masseter function can bebasically recovered one year after mandibular angle osteotomy.