Abstract: The pattern synthesis for opportunistic array radar is designed with the effect of mutual coupling.Active element patterns of an opportunistic array are constructed from those of a small array.Based on this，the intersectional sub-array partitioning technique is needed to divide the antenna array.The generalized mutual impedance matrixes of sub-arrays which are used to build the mutual impedance matrixes of the opportunistic array are calculated with method of moment.Furthermore，genetic algorithm which can optimize the excited state，feeding magnitude and phase of each element is used to synthesize the pattern.In this paper，a uniform plane array and a uniform three-dimensional array are synthesized with this method，and the computational cost is considerably reduced.Moreover，the distance for intersectional sub-array partitioning is given. Simulation results which are compared with the results of the simulation software and the results without consideration of mutual coupling show the correctness of this method and the necessity of considering mutual coupling.