This study focuses on the on-orbit attenuation tracking problem of FY-3B/MERSI. Ocean surface sun glints are adopted as stable targets to track the attenuation from 2011 to 2018. Based on cloud-free and effective sun glint area data, the 865 nm band is regarded as the benchmark band; the ratios between other bands' reflectance and the benchmark band's reflectance are calculated to analyze the attenuations of these bands during the 8 years. There are obvious degradations for all FY-3B/MERSI bands, especially for shortwave bands. The annual degradation rate of 412 nm is 7.12%, while the corresponding value is 0.28% for the 765 nm band. The degradation is much bigger for the 1 030 nm band, at around 3.88%. Furthermore, the reflectance ratios between different bands and benchmark bands show obvious oscillation, consistent with the north-south periodic change of latitude at the center of the sun glint. Ocean surface sun glints are an effective target for the inter-band radiometric calibrations, and could help track the long-term attenuation of on-orbit sensors.