A modified grating light modulator (GLM) device applied to novel micro-spectrometer is proposed,which consists of an upper movable grating and a bottom reflector. When the GLM array is actuated by different voltages,the movable gratings are pulled down to different height,which can modulate lights of different wavelengths. The operating principle,device architecture and fabricated process are introduced,and the device is modeled by using Coventor ware. The electromechanical coupling characteristic is analyzed by the finite element simulation method,the pull-in voltage and response frequency are deduced,and the influence relationship between device architecture and flatness of grating is discussed. The result indicates that flatness of grating can be optimized effectively to achieve better switching modulation feature by increasing the thickness,improving bottom electrode distribution and adopting thinning-folded-beam.