The invention relates to the technical field of energy materials, and discloses a hydrate accelerator and an application thereof in preparing a high-gas-storage-density gas hydrate. The accelerant comprises amino acid and water, and is prepared by well mixing 100 parts by mass of water and 0.05-5 parts by mass of amino acid. The application comprises the specific steps that 100 parts by mass of water and 0.05-5 parts by mass of amino acid are well mixed, such that an accelerant water solution is obtained; the accelerant water solution is placed in an autoclave; high-pressure gas is delivered in under a low temperature; and a reaction is allowed for a period of time, such that the high-gas-storage-density solid gas hydrate is obtained. The accelerant provided by the invention is green and environment-friendly. With the accelerant, hydration induction time can be reduced, gas storage capacity can be increased, and gas storage density can be improved. The accelerant provided by the invention also has the advantages of low price, low dosage, and wide source. The accelerant is recyclable, and has no special requirement on temperature and pressure conditions. The method for preparing the high-gas-storage-density gas hydrate is fast, highly efficient, simple, and easy to realize.