Objective To explore the relationship between abnormal muscle response (AMR) changing characteristics in microvascular decompression (MVD) for hemifacial spasm and treatment outcome after surgery.Methods A retrospective analysis was conducted on 73 patients whose AMR changing characteristics were quantitatively monitored during the whole process of MVD. Before decompression, the AMR threshold of group A1 increased one-fold or more compared with the basic threshold, while that of group A2 increased less than one-fold. After surgery, the AMR of group B1 completely disappeared, while that of group B2 did not disappear. For group B2, the AMR threshold of group B2a increased one-fold or more compared with the basic threshold, while that of group B2b increased less than one-fold. The treatment outcome of each group was comparatively analyzed.Results For 21 patients in group A1, 19 were cured immediately, 1 was cured later, and 1 was not cured; for 52 patients in group A2, 35 were cured immediately, 9 were cured later, and 8 were not cured. The treatment outcome of group A1 was significantly better than that of group A2 (P=0.046). For 50 patients in group B1, 42 were cured immediately, 5 were cured later, and 3 were not cured; for 23 patients in group B2, 12 were cured immediately, 5 were cured later, and 6 were not cured. The treatment outcome of group B1 was significantly better than that of group B2 (P=0.003). Group B2a had a significantly higher cure rate than group B2b (14/16 vs 3/7,P=0.045).Conclusions AMR changing characteristics have important reference significance for surgeons. The treatment outcome would be good in patients whose AMR increases before decompression, completely disappears after surgery, or does not disappear but increases one-fold or more compared with the basic threshold.