Abstract: In order to understand the isosceles triangular subwavelength grating more deeply, the rigorous coupled-wave method was used forin-depth theoretical analysis and research, and the numerical simulation results of isosceles triangular subwavelength grating were obtained. The influence of grating period and incident angle on the characteristics of isosceles triangle subwavelength grating was analyzed, and the high reflection characteristic of isosceles triangle subwavelength grating was explained from the internal magnetic field distribution. The results show that isosceles triangular subwavelength gratings with different grating thicknesses exhibit different characteristics. When the grating thickness is between 0.54μm and 0.57μm, isosceles triangular subwavelength gratings have wide reflection bandwidth, while when the grating thickness is between 0.58μm and 0.66μm, guided mode resonance could be observed. The research can provide theoretical guidance for the preparation of high performance isosceles triangular subwavelength gratings in the future.