We have developed a new technique of surface treatment of RF superconducting cavity by sputtering under ultra high vacuum. In this paper，impacts of sputtering treatment on the surface properties of niobium sample and niobium cavity are analysed in detail. Compared with the traditional “wet" cavity treatment (buffered chemical polishing and electro-polishing)，this dry treatment is simple，easy to control，less costly and without pollution. It is a potential superconducting cavity surface treatment method and can improve the performance of the cavity.