Abstract: A new method of generating ring source by binary grating is described, and the radius and thickness of the source ring can be changed dynamically in either continuous or stepwise fashion. The reason for which the ring source can reduce the coherent noise is given. The relation of the ring sources radius and cavity length with interferogram contrast is deduced. Comparative experiments with the traditional point source show that, the ring source can suppress coherent noises effectively and preserve the fringe contrast. The system intrinsic noise in ring source pattern is less than that in point source one and there is no Newton ring in the phase map in evidence. The improvement of measurement accuracy and repeatability can be achieved with ring source.