The supercoling point, body water and crude fat content in different development stages of sweet potato sphinge, Agrius convolvuli L., in Changsha, Hunan Province were tested, and the relationship between the supercooling point and body water and crude fat content was analyzed. The results showed that the mean supercoling point of larvae increased with the instar increasing, but the mean supercoling point of pupae  decreased. It was found that the mean supercoling point of the 2th instar larvae in all generations was about -11℃, and that of overwintering pupae was -7.38℃, which was lower than the pupae in other different generation. The mean body water content showed decreasing tendency with the development of sweet potato sphinge, and a reverse tendency for the crude fat content. The mean crude fat content of overwintering pupae was 30.23% of its dry body weight. There was positive relationship between supercoling point and body water content, and negative relationship between supercoling point and crude fat content. The results indicated that adjusting body water and crude fat contents in the development may be one of important physiological mechanisms for sweet potato sphinge cold hardiness.