Objective To investigate whether exosomes derived from gastric cancer cells can affect macrophages in tumor microenvironment through miR-151-3p. Methods The expression of miR-151-3p in tumor tissues of patients with gastric cancer and normal tissues was detected by real time quantitative PCR; Gastric cancer cells overexpressing miR-151-3p were constructed, and exosomes were isolated and identified. The expression of CD11b and CD163 markers on RAW264.7 cells co-incubated with exosomes were detected by flow cytometry, and the effects of exosome carrying miR-151-3p on tumor growth and tumor-associated macrophages were evaluated in mice transplanted tumor model. Results The results of real time quantitative PCR showed that the level of miR-151-3p in gastric tumor tissues was significantly higher than that in normal tissues, and the content of miR-151-3p in gastric juice of most patients after operation was lower than that before operation; The content of miR-151-3p in exosomes of tumor cells overexpressing miR-151-3p was also significantly higher than that of untransfected cells. Exosomes carrying miR-151-3p can induce phenotypic differentiation of M2 in co-incubation with RAW264.7 cells. Similarly, tumor transplantation model also showed that exosomes carrying miR-151-3p can induce tumor-associated macrophages to polarize to M2 and promote tumor growth. Conclusion miR-151-3p derived from gastric cancer exosomes can induce the polarization of M2 macrophages and promote the growth of gastric cancer. The treatment of miR-151-3p may destroy the tumor microenvironment of immunosuppression, which assists the anti-tumor immunotherapy.