Objective To solve the immersion tin problems existing in chloride system and sulfate system. Methods This paper used tin methane sulfonate as main salt and thiourea as complexing agent to immerse tin plating onto copper powder. And the influences of thiourea concentration, tin ion concentration, methyl sulfonic acid addition and bath temperature on the microstructure of tin plating were studied. Results The results showed that the tin ions could form complex ions with thiourea, which would reduce the equilibrium electrode potential of tin ions, and make it possible for immersion tin plating to immerse onto copper powder in methyl sulfonate system. Conclusion When the tin ion concentration was 0. 15 mol / L, the thiourea concentration was 0. 80 mol / L,the concentration of methane sulfonic acid was 50 mL / L, the solution temperature was 75 ℃ , a uniform and dense tin coating with a good combination with copper surface could be obtained.