An analysis is made of the dates of last days for daily mean temperature being stably greater than 22 ℃ in use of the data from various stations of Wenzhou, and the variation characteristics and trends are obtained. To judge the objectivity of the variation, a significance test is conducted with SPSS (Statistical Product and Service Solutions). The results show that the dates of the last days for daily mean temperature being stably greater than 22 ℃ at some stations varied obviously after the 1990s. Under the condition of 80% assurance rate, the dates of the last days before and after 1990 are studied. The safe fullheading periods are determined, and the sowing dates are derived. The suggestions of sowing dates for doublecropping late rice are presented, which can be used as references for the better utilization of agricultural climatic resources.