In this paper, we describe the structure of Micromegas (micro mesh gaseous structure) detector which has been developed recently by our group. And its count plateau, gas gain and energy resolution in the condition of a Fe-55 X-ray source and various Ar-CO2 mixtured gases are plotted as functions of mesh voltage. Based on the experimental results, we confirm that we have mastered the technique of fabricating this kind of detector with high energy resolution and excellent performance.