Abstract: In this paper, a topology optimization based design method for pattern synthesis of thinned antenna arrays is proposed. The optimization formulation is appropriately established and effectively solved by using a gradient-based algorithm. In order to rigorously consider the mutual coupling effect among the coupled array elements, the full-wave method of moments is well integrated into the optimization design to calculate the accurate radiation pattern for guaranteeing the effectiveness of pattern synthesis. The tangential interpolation function of metallic material with a pseudo resistance is introduced to help the self-penalization of the optimization design to obtain 0-1 solutions. Based on the method, thinned solution of typical coupled arrays with both the element number reduction and peak sidelobe level suppression is obtained.