Effects on microstructure and property of Sn-9Zn solder alloy were researched under different magnetic field intensity by means of XRD,Leica and Microhardness, etc. The result shows that external magnetic field can promote microstructure refinement of Sn-9Zn solder alloy, but can't change its phase. Wetting ability and microhardness of Sn-9Zn solder alloy enhance with increasing intensity of external magnetic field, and microhardness of Sn-9Zn solder alloy reach to 22.9 MPa at 0.5 T of external magnetic field, which increases 13.2% compared with no external magnetic field action to the solder.