A significant yet not widely realized topic is analyzed when the field-widened Michelson interferometer (FWMI) is used as a spectroscopic filter in high spectral resolution lidar (HSRL), that is, tolerance evaluation for anti-reflection (AR) coating reflectivity of the FWMI. Since AR coatings on the interface of different materials in the FWMI cannot be with 100% transmittance, a part of the radiation would be reflected back once the light passes through these surfaces, and these reflected lights would be further reflected many times in the interferometer as stray lights. The influence mechanism on the FWMI performance due to the multi-reflection caused by AR coating reflectivity is analyzed, and an iterative algorithm is proposed to estimate the relationship between the performance of the FWMI and the reflectivity of the AR coating quantitatively, using the spectral discrimination ratio (SDR) as the performance metric. Results show that the reflection induced by AR coating will degrade the suppression ability of the FWMI to the aerosol scattering while it imposes no effect on the molecular transmittance. The overall consequence is to make the SDR of the FWMI decrease. This method can provide considerable reference for the tolerance evaluation of AR coating reflectivity in FWMI, and is one of the important aspects that can guarantee good design performance of the FWMI.