The invention provides a method for preparing gas hydrate accelerant, which takes a high pressure gas cylinder as gas source; the high pressure gas cylinder is regulated to have proper pressure by a pressure regulating valve, and the consumed natural gas is calculated by a mass flowmeter; the temperature and the pressure in a reactor are monitored by a pressure and temperature transmitter; thermostatic waterbath is used for controlling the temperature of the liquid in a trough, thus regulating the temperature in the reactor; a data acquisition system and a computer are used for collecting data, and an opto-electrical lens is used for monitoring the forming situation of hydrate in the reactor. The composite accelerant is low in cost and little in dosage, ensures the generating condition of the hydrate to be reduced, the time to be shortened and the gas storage quantity to be increased, and effectively improves the economic benefit of the production of the hydrate.