Abstract: Ant colony optimization(ACO)algorithm is applied to synthesize the array antenna pattern by controlling only the current amplitudes.In order to overcome the drawbacks of the standard ACO,such as premature convergence and difficulty in dealing with optimizing continuous variable(e.g.the current amplitudes),a modified ACO algorithm is proposed.The technology of nonintegral encoding and the method of optimization in vicinity are adopted in the modified algorithm,which can optimize continuous variable and improve the convergence speed and accuracy. The simulation results are presented to show that the modified algorithm may obtain better results than those reported in other literatures.