An anti-glare rearview mirror assembly and a reflectance control method thereof are disclosed. The assembly includes an electrochromic rearview mirrors, two rearward light sensors, and a comparative controller. The sensors receiving a first rearward light from a first specified region and a second rearward light from a second specified region at the same time point, respectively, wherein the first and second specified regions partially overlap with each other. The intensities of the first and second rearview mirror light are compared to obtain a light difference. The reflectance of the anti-glare rearview mirror is adjusted according to the light difference.