A stannate conversion coating was prepared on the AZ91D magnesium alloy surface by a chemical conversion process. The coating performances were tested by CuSO4 drip experiment, EIS, Tafel, SEM and XRD. The effects of some organic additives including tartaric?acid, citric?acid, phytic?acid, EDTA, and sodium?dodecyl?sulfate on the coating corrosion resistance were studied. The results show that the drip time is increased from 35 to 86 s by adding sodium?dodecyl?sulfate and it could improve the corrosion resistance of the film to a large extent. The morphology of the membrane layer mainly contains MgSn(OH)6 and Mg(OH)2 which is granular-bonded