Abstract: Stainless steel 304 is one sort of the austenitic stainless steel for most extensive use.It has excellent corrosion resisting and fire resisting property, high hypothermic strength and fine mechanical property.Its welding method is TIG in common use.The TIG welding method is an inefficient welding method because of its shallow penetration and low welding speed, the grain size of the weld is also inclined to grow up which may reduce the performance of the weld.Ultrasonic treatment is an effective way to minimize the grain size and improve the microstructure in the process of metal freezing.Ultrasonic treatment was lead in the process of TIG welding of stainless steel 304 to increase the welding efficiency and improve the weld property.Build-up welding experiments were taken on the flat plate.The results showed that the weld penetration and depth-to-width ratio increase and the crystallizing mode change from columnar crystals to small dentrite equiaxed crystals.Also, the grain size reduce and the organization of the fusion area is uniformed.