Climate warming in the North China Plain (NCP) is expected to greatly affect corn production. On the basis of a comprehensive consideration of the double-cropping system, we investigated the impacts of climate warming in the past 55 years on the planting boundaries and areas of varieties of summer corn with different maturity levels. In addition, we tried to explore the probable reasons for the changes in planting boundaries. Climate warming caused a northward shift in the planting boundaries of summer corn, resulting in the expansion of the total planting area. However, the trend for the planting area of each belt of corn maturity was not always consistent. Because of the advanced planting date and delayed physiological maturation date, the growing season of corn in the NCP has been prolonged in the past 55 years. Climate warming also increased the active accumulated temperature with a threshold of 10° (AAT10) during the corn growing season by 73.2°C decade−1, which was mainly caused by the increase in the number of days with a daily temperature over 10°C. In summary, the planting boundaries of varieties of summer corn with different maturity levels have greatly changed due to climate change, and corn production in the NCP could benefit from climate warming through the greater planting area and longer growing season.