Abstract: Materials experienced mild wear in incubation period and responded cavitation in terms of elastic/plastic deformation or grain pull-out. The way of response varied with the type of material. In order to understand the incubation period, ways of surface roughness measurements and light microscope observations have been established through the study of material response, worn surface morphology and their relationship in incubation period. The present study evaluated resistance to cavitation erosion of three materials including pure Cu, nickel-base alloy Hastelloy C-276 and Sialon ceramic using a standard ultrasonic vibratory cavitation erosion apparatus and focused on the evolution of surface roughness parameters (roughness R_a and Core roughness depth R_k) and area fraction of cavities of the three materials in their own incubation period. R_a and R_k were very sensitive to plastic deformation of pure copper and Hastelloy C-276 in the incubation period, but not always to early material removal. R_k had a similar curve with R_a in the whole process of cavitation, and its trend was more obvious. R_k was a better surface roughness parameter to reflect the surface change in incubation period and the whole cavitation process than R_a. Furthermore, it could reflect the extent of plastic deformation of different metal in incubation period. For Sialon ceramic, R_a and R_k remained nearly unchanged in the incubation period while area fraction of cavities presented an approximate linear growth trend in the same stage. The incubation period was dominated by creation of cavities, along with growth of a small amount of cavities. Area fraction of cavities was an appropriate parameter to describe surface changes in the incubation period of ceramics.