At present, there is a wide demand for single-pole multi-throw switch in communication, navigation and other fields. However, this kind of switch is usually large in size, narrow in working frequency band, large in insertion loss and low in isolation. A series-contact double-sided multi-contact RF MEMS single pole six throw switch was designed to solve the above problems in this paper. Three circular contacts were placed on the lower electrode of the switch, and the distal end was connected with a horn shaped transition belt. Above it were "X" shaped upper electrodes with slot. This structure could improve RF performance greatly by reducing coupling capacitance and contact resistance. HFSS software was used to simulate and optimize the switch. Its operating frequency can cover L~Ka band. At 26.5 GHz, the insertion loss is less than or equal to 0.3 dB, and the isolation degree is more than or equal to 37 dB. In addition, its size is 1.05×1.05×0.5 mm3.The results show that the proposed single pole six throw switch has great RF performance and meets the requirements of miniaturization. Therefore, it has a large application prospect in L~Ka band navigation, cognitive radio network and microwave testing.