A broadband reflector with a reflectance up to 97.8% over a 144 nm spectral range from 1476 to 1620 nm was proposed by comprising double-layer subwavelength gratings with one grating layer embedded in SiO2 layer. An analysis of the resonance leaky modes with overlapping gratings showed the physical mechanism of the wide broad high-reflectivity band. The structural parameter tolerance was analyzed and the variation of bandwidth was explained by combining the behaviors of the two guided mode resonances. The guided mode resonance and high refractive index contrast properties led to a good angular tolerance that exhibited an angular insensitivity (~ 11°) at 1550 nm. Overall, the broadband reflector may benefit the monolithic integration of optoelectronic devices.