The nanocrystalline Mg2Ni-type alloys with the compositions of Mg20Ni10-xCux (x=0, 1, 2, 3, 4) were synthesized by melt spinning technique. The microstructures of the alloys were characterized by XRD, SEM and HRTEM. The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system, and their hydriding and dehydriding kinetics were measured by an automatically controlled Sievert's apparatus. The results show that all the as-spun alloys hold a typical nanocrystalline structure. The substitution of Cu for Ni improves the electrochemical hydrogen storage performances of the alloys significantly, involving both the discharge capacity and the electrochemical cycle stability. Furthermore, the hydrogen absorption capacity of the alloy first increases and then decreases with the rising of Cu content, but the hydrogen desorption capacity grows dramatically for the same reason