In order to improve the hydrgen storage properties of LiAlH4 and LiNH2, LiAlH4/2LiNH2 composite was prepared by ball milling LiAlH4 and LiNH2 with a molar ratio of 1:2. The hydrogen storage properties and the microstructure change during dehydrogenation process were studied by using TG/DSC/MS, XRD, FTIR and NMR. Based on the hydrogen desorption properties and microstructure analysis, the dehydrogenation mechanism of LiAlH4/2LiNH2 composite was discussed. The experimental results show that the dehydrogenation reaction path of LiAlH4 is changed by addition of LiNH2, and the final product is Li3AlN2.