Through the analysis of spring(April to May)low temperature occurrence from 1966 to 2003 in Nanzheng, by applying <12℃ negative effective accumulate temperature and minimum temperature to classify damage extent of low temperature to rice seedling. The results show that the occurrence of <12℃ low temperature are all in April, 30% years have no damage, 21% years have light damage,19% years have middle damage,21% years have severe damage. The reverse spring cool occurrence frequency is 20%, center on the first and second decade of May. <12℃ low temperature belong to continuous overcast and rainy type times are as two times as belong to sunshine and cold ones. The reverse spring cool occurrence years are usually accompany with continuous overcast and rainy type low temperature. The impacts of low temperature to rice seedling are analyzed, the results show that the middle and third decade of April are the crucial period of <12℃ low temperature damage, the first and second decade of May are the crucial period of reverse spring cool damage. Aiming at different type of low temperature corresponded forecast-serve and field manage measures are raised.