The invention discloses an Li-N-H system hydrogen storage material and a preparation method thereof. The Li-N-H system hydrogen storage material is prepared from LiNH2, LiH and a small quantity of alkali metal sulfate additive. The preparation method comprises the following steps: by taking the LiNH2 and the LiH with the molar ratio being 1 to 1.1 and the additive with the molar percentage content being 0.5-5 mol percent, carrying out ball milling treatment at the 1MPa hydrogen atmosphere under the condition of shielding gas to prepare the Li-N-H system hydrogen storage material. The invention develops a novel Li-N-H system hydrogen storage material with rapid hydrogen desorption speed and good cycle stability, so that the hydrogen desorption peak temperature of an Li-N-H system is lowered by 25-39 DEG C, the hydrogen absorption and desorption dynamic performance of the Li-N-H system is effectively improved, and practical course of the storage materials in the type is effectively promoted. The preparation method of the material is simple and feasible in operation, cheap and available in additive and low in preparation method and has an industrial prospect and an application value.