Abstract: Nanocrystalline nickel coatings were prepared by pulse jet electrodepositing on the substrate of 45 carbon steel.The effects of average current densities on the surface morphology,microstructure and average grain sizes of nickel coatings were studied by SEM and XRD,and the corrosion resistance was also tested.The results show that the nickel coatings prepared by pulse jet electrodepositing have smooth surfaces,fine grain sizes and good compact quality.However,there are still some pores between grains.With the increase of average current densities,average grain sizes of nickel coatings become finer and then bigger.Using optimum process parameter of average current density of 39.8 A·dm-2,a coating with the best compact quality and finest average grain sizes (13.7 nm) is obtained.After pulse jet electrodeposition,the corrosion resistance is obviously increased,but after some time the corrosion rate increase,which might be greatly related to the infiltration of corrosive media.