Abstract: The effect of hydrogen gas pressure,synthesizing temperature and the temperature holding time on the product of Mg₂NiH₄ is investigated and the product is analyzed by using XRD and SEM. It is manifested that combustion in argon atmosphere for one hour at the temperature near to the eutectic point of magnesium and nickel,plenty Mg₂Ni is formed and the combustion reaction is reaching complete as holding the temperature for two hours.The quantity of magnesium nickel hydride increases evidently with the boosting of hydrogen gas pressure and the nickel tends to become disappeared under the hydrogen gas pressure 2.2MPa.The quantity of magnesium nickel hydride increases with the rising of synthesizing temperature,but overtemperature is not advantageous to the formation of Mg₂NiH₄ from Mg₂NiH_0.3 and holding the temperature for a proper time is advantageous to the synthesizing reaction of magnesium and nickel.