The Mg2NiH4 hydrogen storage material was successfully prepared by controlled hydriding combustion synthesis (CHCS) from Mg and Ni powders in a high magnetic field. The effects of magnetic intensity on the structure, phase compositions and the hydriding/dehydriding (A/D) properties of the composite are investigated. As a result, a high magnetic field promotes the formation of Mg2NiH4. The PCT results show that the maximal hydrogen capacity at 573 K is 3.59 wt.%. The comparison of the hydrogen A/D results under the different conditions suggested that 4 T is the optimal magnetic intensity in our trial.