Abstract: A method for reverse design of the resonance-domain rectangular-groove dielectric grating based on modal method is presented. The design of the polarization (non-polarization) beam splitter and blazed grating is discussed. As an example, the -1st transmitted order blazed grating with fused-silica is designed with the reverse design method. The basic idea behind the method is the excitation and propagation of the propagating modes in gratings. As different phase difference is accumulated for the first two propagating modes excited in gratings, the incident light can be diffracted into the -1st or 0th order with about 100% diffraction efficiency for TE or TM polarization. The diffraction efficiency of the -1st transmitted order blazed grating is calculated with the rigorous couple-wave analysis (RCWA) method. The geometrical parameters of the blazed grating calculated by the modal method agree well with the results simulated by RCWA.