According to the application of laser, the distribution of the light intensity usually need shaping. The most important element is diffractive optical element (DOE). adaptive-additive (AA) method is applied and ameliorated, which conquer the two bugs of AA method and improve the precision. A procedure of auto selecting parameter is added in the AA method, in order to reduce the workload of designing. Several ways are proposed to solve the possibility appearing of zero in the denominator. At last, a DOE is designed to shape Gaussian light to square distribution light as well as a grid to divide light, and the results are good. Compared with the AA method, the Gauss method shows its merit. All of these prove the feasibility of the AA method for DOE designing.