A new design method of diffractive microlens array for laser beam uniformity adopting optimization procedure in Zemax is proposed. The custom optimization function in Macro language is created by means of energy mapping in non-imaging optics. A microlens array and a condensing spherical lens are used as the homogenization optical components in the system. The aspheric surface of the lens unit of the microlens array is automatically optimized in sequential mode of Zemax software, and a 6 mm×6 mm square spot with the irradiance uniformity greater than 90% and the energy efficiency of 83% on the target surface is realized. The design results are verified by TracePro simulation program. This method is valid and convenient in the system design of the microlens array for laser beam uniformity, without the need for the complex calculation and the repeating adjustment of the system parameters in the traditional method.