Based on design type of surface spillway of TGP,the caviation characteristics was studied by means of vacuum tank test,in which dete ction technques of underwater noise were adopted.The results indicate that the W ES profile spillway is cavitationfree type,weak cavitation occurs at the end o f the bucket lip but possibility of cavitation erosion is negligible,steam cavit ation appears in area of the working gate slot and becomes intensive with increa sing working head.Local configuration of double gate slots were modified by expe riments and the cavitation characteristics were improved clearly.In order to van ish the cavitation completely,further optimization must be made.