Abstract: The spreading properties of Sn-Cu-Ni solder on 304 stainless steel sheet were studied by matching different fluxes, and the results indicated that Sn-Cu-Ni solder has excellent spreadability when it is matched with newly developed flux of H36. Its spreading area reaches 109.56 mm²,which is increased by 249.4%,239.3% compared with fluxes of H₃PO₄-C₂H₅OH and ZnCl₂-NH₄Cl,respectively. Results also indicated that the emulsifier 6500 can further improve the spreadability, and the largest spreading area reaches 157.49 mm². It was found that,when the optimized flux H36-2 is matched with Sn-Cu-Ni as solder for 304 stainless steels,the mechanical properties of the soldered joints are superior to the existing literature data,the tensile strength and shear strength of the joints reached up to 22.72 MPa and 33.93 MPa,respectively.