Abstract: The overcooling phenomena are very common in inorganic thermal storage materials. This paper mainly studied the overcooling phenomena of dibasic sodium phosphate. Adding an appropriate amount of anti-overcooling agent could reduce its overcooling. The experimental result indicated that，adding aluminum oxide had very good effect to reduce the overcooling of dibasic sodium phosphate，with the phase transformation temperature kept at 35—36℃，and the phase change process could also be maintained for a long time. At the same time，adding some carboxymethylcellulose sodium as thickener not only could improve the stability of thermal storage system，but also could reduce the overcooling.