According to the requirement for film thickness profile along the radius in the graded reflectivity mirror, which is used in the designed single transverse Nd∶YAG laser resonator, a designing method for mask is introduced, which is used for depositing graded reflectivitymirror. A specialmask with circle aperture is analysed firstly , the film thickness profile by using circle aperturemask and the target profile is compared, and the mathematic model for accurately designingmask is built accordingly. The method for designingmask is put forward, and the aperture size and the position are computed by program. The film thickness profile along the radius of the varying layer is almost the same as the target profile by using it.