This paper presents a novel variable speed constant frequency doubly fed salient pole synchronous machine by patent. It deals with basic theory and construction of variable speed salient pole synchronous machines, especially on variable speed constant frequency characteristics. The split salient pole and orthogonal winding are adopted in rotor. The structure of the rotor is simple and tried. Variable frequency converter at rotor supplies the excitation winding. It makes machine to achieve good character of variable speed constant frequency. Experiments show that the patent is correct and practical through prototype test. It will be widely applied to large waterpower and wind power generators.