The work aims to develop a new type of composite cold storage agent based on the temperature control demand from storage and transportation of fruits and vegetables. The cold storage agent was prepared by using mannitol solution as a base and adding sodium carbonate and CMC. The thermophysical property and the long-term performance were measured by DSC and solidification curve and melting curve method, and finally the optimal solution was screened out. The final formula of the cold storage agent was 5% mannitol, 2% sodium carbonate, 3% CMC, and the rest all water. The cold storage agent phase change latent heat was 292.5 kJ/kg, and onset temperature (initial melting temperature) was −4.5 ℃.Thawing through long-term experiments showed that the cold storage agent had good stability and there was no subcooling and phase separation. In conclusion, the cold storage agent has high latent heat, good stability and long-term repeated use, thus it can be applied to fruit and vegetable storage and transportation fields.