Abstract. In this paper, the classic PSO algorithm is applied to the pattern synthesis of antenna array using 4-bit digital phase shifters. In order to directly apply the existed PSO algorithms to the pattern synthesis using digital phase shifters, this paper proposes a simple truncation rounded number strategy to transfer the discrete problem to the continuous one, which not only produces no quantization error, but also avoids the limitation of the discrete PSO algorithm. The optimized results are better than that of the discrete PSO algorithm.