Objective To explore the mechanism of miR-381 on the infiltration of polymyositis (PM) macrophages by targeting stromal cell derived factor-1 (SDF-1).   Methods PM model mouse was constructed by rabbit myosin (1.5 mg), mycobacterium tuberculosis (5 mg) and pertussis toxin (500 ng). The 30 PM model mice were divided into control group and PM+miR-381 group (n=15/group). During the same period, 15 healthy mice were used as a control group. Mice in the PM+miR-381 group were injected with miR-381 agomir (300 μg) intraperitoneally for 2 weeks. Serum creatine kinase (s-CK), interleukin (IL)-1β and IL-6 levels in serum of each group of mice, and the pathological changes of muscle tissue were detected and compared. The macrophage marker protein F4/80 was detected by immunohistochemical staining to assess the infiltration of macrophages. The expression levels of miR-381 and SDF-1 mRNA and protein in muscle tissues of each group were detected. The target relationship between miR-381 and SDF-1 was verified by dual luciferase report. Mouse macrophages were divided into miR-381 NC group and miR-381 mimic group. The SDF-1 mRNA and protein levels in each group were detected by Real-time PCR and Western blotting. Transwell was used to detect the level of cell migration to evaluate the infiltration capacity.   Results The above indicators of the three groups were significantly different (P<0.05). The level of miR-381 in the muscle tissue of the PM group was significantly lower than that of the control group, s-CK, IL-1β, IL-6, histological score, macrophage infiltration, and SDF-1 mRNA and protein expression levels were significantly higher than those of the control group (P<0.05). The level of miR-381 in the muscle tissue of the PM+miR-381 group was significantly higher than that of the PM group, s-CK, IL-1β, IL-6, histological score, macrophage infiltration, and SDF-1 mRNA and protein expression levels were significantly lower than those in the PM group (P<0.05). The dual luciferase report result  indicated that miR-381 could target binding to SDF-1. The expression levels of SDF-1 mRNA and protein in macrophages in the miR-381 mimic group were significantly lower than those in the miR-381 NC group (P<0.05). The number of migrating cells in the miR-381 mimic group was significantly lower than that in the miR-381 NC group (P<0.05).   Conclusion Increasing the level of miR-381 can inhibit the inflammatory infiltration ability of macrophages by targeting the expression of SDF-1, thereby alleviating PM.