Abstract: In view of the fact that the freezing damage to late maturing citrus in Chongqing in recent years is not only related to the low temperature and its duration, but also to the site conditions. Based on some examples of freezing damage, the index of freezing damage to late maturing citrus is established by using information diffusion theory. The result shows that the evaluation grade of freezing damage degree by using this index is more consistent with the actual situation, and it is more in line with the actual situation of Chongqing than the lowest temperature judgment grade. This index can be applied to the monitoring and evaluation of freezing damage to late-maturing citrus in overwintering stage in Chongqing, and has certain popularization value.