Abstract: Based on a numerical model cesium atomic clock designed before,the influence of atomic velocity distribution consisting of two peaks and three peaks has been studied respectively.The main characteristics of the microwave spectra under this circumstance has been analyzed and compared with the reported phenomenon in NBS-4 magnetic state-selection cesium clock and the recent experimental result of an optically pumped small cesium clock in Peking University.The characteristic of the microwave spectra in the case of atomic velocity distribution consisting of two peaks has been verified.