In order to tackle the key problems in the experimental study on the microwave plasma thruster, of which the whole system operates under the vacuum condition, and remove the unnecessary energy loss, an electro microwave device operating under atmosphere and vacuum condition has been developed by applying the design technology of the nonlinear power supply, the integration of attenuator and detector, liquid cooling, and after resolving the gas breakdown problems of electro and microwave apparatus. The experimental study on the device with argon and helium as propellant has been carried out. The results show that the output power of microwave is stable， the device can operate under vacuum and atmosphere condition reliably.