With the continuous development of the micro-structure of gas detectors, many different new detection requirements have been proposed. For more stable working time, lower discharge rate with long term and high effective gain, a new structure detector has been designed. Combined with the detection's advantages of MicroMegas and gas electron multiplier (GEM), it is composed of a MicroMagas chamber with one GEM foil as preamplifier. In this paper, the structure of the detector and detection principle are presented in detail. Using a 55Fe X-ray radioactive source in the operation mixtures gas of argon and isobutene (Ar/Iso =95/5), the performances of the detector gain, discharge rate, energy resolution and stable working time are investigated. Compared with standard MicroMegas detectors with no GEM foil, our detector show that a stable working time could reach more than 30 h of continuous work, the gain of the detector could exceed 106 and the discharge rate could be reduced by nearly 100 times at the same gain.