Abstract: The effect of pretreatment techniques on the corrosion resistance of stannate conversion coating of AZ91D magnesium alloy was studied by measuring the average corroison rate of it in total immersion test.The surface morphology and phase structure of the stannate conversion coating of AZ91D magnesium alloy were investigated using SEM and XRD.The results show that corrosion resistance of the stannate conversion coating pretreated as following process:acid pickled by phosphate first,then alkaline pickled by sodium hydroxide,trisodium phosphate and sodium carbonate,was the best.