Optimized planting date is necessary for field crops to obtain the highest yields. From the perspective of the thermal resources required by maize maturity, this paper introduced a method to determine the latest planting date. Based on the weather station temperature data, the beginning date to plant, latest planting date as well as the spatial-temporal changing characteristics of the maize planting date during 1971 to 2000 were investigated. The results showed that for the most parts of Liaoning province the beginning date to plant was during mid-ten-day in April to last-ten-day in April. During the 30 years, the trends of the beginning day to plant for the whole province was not prominent except for the east and the north part of Liaoning province showing earlier at a rate of 2 d?10a-1. The trends of the first frost date showed delayed in Liaoning province and the average changing rate was 1.6 d?10a-1. The latest planting date was during the end of first-ten-day in May to the beginning of mid-ten-day in May. The delay of first frost date combined with climate changing warming made the rate of climate trends of latest planting date was 4.0~5.0 d?10a-1. At last, the adaptable breed and the time range for optimized planting of each district in Liaoning province were listed in this paper, which may provide a reference in field crop production.