Abstract: An optimization method of grid ring radii based on modified genetic algorithm is presented under the constraints of fixing the aperture, the number of elements and the minimum element spacing. We make element spacing on the same ring equal, and make use of modified genetic algorithms(MGA) to optimize grid radii to minimize peak sidelobe level. The proposed method can improve performance of sidelobe level(SLL) of the sparse concentric ring arrays and can meanwhile relatively reduce computational cost. Finally, the simulation results confirm the great efficiency and robustness.