Mgx/Mg2Ni(x=10%, 30%, 50%) composites were synthesized by ball milling the mixture of Mg2Ni alloys and Mg powder. XRD analysis show that no new phase was produced, and the decomposability of Mg2Ni phase existed in the milling of solo Mg2Ni alloys is restrained in the milling of Mg2Ni alloys and Mg powder. Electrochemical characteristics of Mgx/Mg2Ni composites at different milling time were evaluated by simulated battery test. It was found that the discharge capacity of Mgx/Mg2Ni composite was obviously improved with increasing content of Mg powder in the milling. The discharge capacity of the composites were enhanced with increasing milling time at the beginning of milling, while a decrease was followed. The relationship between discharge capacity and milling time was mainly influenced by the micstructure of composites caused by ball milling.