Some advantages and important application of the testing method for optical supersmooth surface using atomic force microscope (AFM) are discussed. Some testing results of microprofile and micro-defect with nonometer-grade for optical supersmooth surface using AFM method are presented, and the change of morphology and micro-roughness before and after coating of same surface is given. For comparison, testing results of micro-roughness parameters for same surface measured using interference profiler are presented too. It is indicated that AFM method has three-dimensional high-accuracy, but interference method has only one-dimensional, so the former can give true morphology and microprofile of surface.