A novel micro-opto-electro-mechanical system(MOEMS)-based light modulator for laser project display is proposed,which is called grating moving light modulator (GMLM). It can modulate light by diffraction,and has a simple fabrication process and projection optical system. The light modulation theory and the projection optical system of GMLM are introduced. The optical model of GMLM is found to deduce the Fraunhofer diffraction pattern through the projection optical system based on the scalar diffraction method. The static and dynamic projection experiments of GMLM array are completed by the projection demo system. The results demonstrate the operation and projection principle of GMLM.