Dense phase carbon dioxide (DPCD) is a promising non-thermal sterilization technology. In order to explore the effect of DPCD on the quality of casein in dairy products. We took casein as the research object and studied the effect of DPCD treatment pressure， time and temperature on the structure and physical properties of casein. The secondary and tertiary structure changes of casein are characterized by circular dichroism and surface hydrophobicity. And the effect of DPCD on the physical properties of casein such as interface properties and flow behavior are reflected by solubility， particle size， emulsibility and viscosity. The results show that when the treatment temperature and time are constant， increasing the DPCD treatment pressure will cause more α-helices and random coils to be converted into β-sheets in the secondary structure of casein， improve its surface hydrophobicity， and reduce its solubility and apparent viscosity， at the same time make its particle size and emulsibility first decrease and then increase. The effect of treatment time on casein is similar to pressure， but its effect on apparent viscosity is not significant； When the treatment pressure and time are constant， increasing the DPCD treatment temperature may cause the opposite change in the secondary structure of casein， and make its surface hydrophobicity increase first and then decrease， at the same time cause the reduction of its solubility， emulsibility and increase its particle size sharply. In summary， the pressure， time， and temperature of DPCD treatment affect the structure and physical properties of casein， among which temperature has the most significant effect. Therefore， the low temperature treatment conditions can effectively protect the quality of dairy products after DPCD treatment.