Amorphous Mg-Ni alloy was prepared by mechanical alloying (MA). The state of the amorphous phase was analyzed by X-ray diffraction (XRD). The hydrogen desorption capabilities and electrochemical properties were tested. The analysis of the relationship among the ball-milling parameters, microstructures and properties of the alloy showed that the milling velocities have a critical influence on the formation of Mg-Ni amorphous phase. The higher the milling velocity is, the less the forming time of the amorphous phase is. And with the increasing of the ball-milling time, the amount of Mg-Ni amorphous phase increases. Whereas the hydrogen desorption capabilities and electrochemical properties will decrease if the alloy is ball-milled for a long time after the complete amorphization occurs. Mg, Ni atom ratio also has some obvious influence on the formation of the amorphous phase and the properties of the alloy. Increasing the content of Ni appropriately will improve the efficiency of formation of the amorphous phase, the hydrogen desorption capabilities and electrochemical properties of the alloy.