Based on grating electromagnetic theory, initial values of the grating groove were computed with grating equivalence rule. The design was then optimized with the diffraction efficiency contour method. Gratings of arbitrary groove shape with a geometry symmetry center can be designed in this way. As examples, four kinds of groove gratings were designed and fabricated with groove shapes of sine, rectangle and trapeze. The peak efficiency of TM mode for sine groove grating is 95% theoretically and 92% experimentally in C band.