With the original worm grinding method to manufacture face-gear, the mathematical models of shaper, worm, and face-gear are established at the beginning. Subsequently, a problem of the original grinding method is illustrated that the working part of the face-gear tooth surface may not be covered completely. To overcome this problem, multistep grinding method for completely grinding the whole working part is proposed by studying contact lines of the tooth surface and singularities of the worm thread surface. The proposed method is verified in matlab with theoretical analysis. Finally, the simulations of the original method and the multistep method in the vericut software verify the feasibility and correctness of the proposed method. The study provides an effective and precise approach to grinding the face-gear.