The Aerosol Optical Depth（ AOD） retrieval algorithm for sand-dust weather over ocean is investigated u sing FY-3A /Medium Resolution Spectral imager（ MERSI） based on aerosol modes in the MODIS C005 over-ocean algorithm. The AOD（ 550 nm） retrieved from MERSI is evaluated with MODIS AOD product（ MOD04）. Results show a systematic bias in this algorithm. Further analyses reveal that this bias results from the MODIS-available aerosol modes. Therefore

a sand-dust aerosol mode is adopted to modify the MODIS aerosol modes by mixing them at an appropriate ratio. AOD is retrieved a second time based on the modified aerosol modes

and the corresponding results exhibit good consistency with MOD04

indicating that modified aerosol modes are more appropriate for the AOD r etrieval from MERSI for sand-dust weather over ocean.