A micromachined optical modulator called grating light modulator (GLM) with electrostatic actuation, fabricated by the conventional process, is described. GLM modulates the light energy by changing the distance of the movable grating and the underlying fixed reflector, which can be applied in projection display in four-focus optical system. With the typical four-focus optical system, the projection display optical system based on GLM is optimized and designed, which is analyzed by Fresnel diffraction. The static and dynamic display experimental systems are designed. The experimental results indicate that the GLM technique has characteristics that make it suitable for projection display applications and several characteristic measurement experiments can be carried on by using such system, such as the working voltage, the pull-in voltage, the response frequency and so on.