Abstract: The cavitation erosion behaviors of 304 austenitic stainless steel base metal and welded joint had been investigated in Pb-Bi eutectic alloy at 550 ℃ with an ultrasonic vibratory instrument. The surface morphology of the base metal and welded joint after different cavitation erosion at different time was observed by a scanning electron microscopy (SEM), the surface roughness of the samples after cavitation erosion was analyzed by an atomic force microscopy (AFM).The results indicated that the cavitation damage on the surface of base metal and welded joint was more serious with cavitation time being increased. With characters of the structure inhomogeneity and composition segregation, welded joint had the weak zone in the structural material. During the cavitation erosion process, the surface roughness of the base metal increased from 0.098 μm to 0.460 μm, and the surface roughness of the welded joint increased from 0.117 μm to 0.599 μm.