Abstract: An investigation on the effects of additives in direct contact ice thermal stora ge system which were very effective in direct contact gas hydrate thermal storage system was conducted by experiments. Among five additives, such as NaCl,CaCl ₂,zinc powder,iron powder and butyl alcohol, it was found that zinc powder h as the best effect on volumetric heat transfer coefficient and butyl alcohol has no effect.It was also found that volumetric heat transfer coefficient increased with increasing quantity of iron powder and NaCl,while decreasing quantity of b utyl alcohol and zinc powder.The pattern of temperature distribution in cool storage cylinder has hardly any difference with increasing quantity of additive.From the investigation,it can be concluded that solid additives have the best resu lt on the direct contact ice thermal storage system.