This paper is concerned with the research on the rational curve for the bucket of a spillway. A new type of rational curve against cavitation damage to spillway has been proposed; and the numerical results show that the proposed curve (gradually and continuously varied curvature curve, abbreviated as GCVC curve) can greatly raise the minimum cavitation number and cause the distribution of water pressure on the curved surface more reasonable. The proposed curve (GCVC curve) is simple, and can be conveniently used in practical hydraulic engineering.