Clarification of influencing factors (cultivar planted, cultivation management, climatic conditions) affecting yields of summer maize (Zea mays L.) would provide valuable information for increasing yields further under variable climatic conditions. Here, we report actual maize yields in the Huanghuaihai region over the past 50 years (1957-2007), simulated yields of major varieties in different years (Baimaya in the 1950s, Zhengdan-2 in the 1970s, Yedan-13 in the 1990s, and Zhengdan-958 in the 2000s), and factors that influence yield. The results show that, although each variety change has played a critical role in increasing maize yields, the contribution of variety to yield increase has decreased steadily over the past 50 years (42.6%-44.3% from the 1950s to the 1970s, 34.4%-47.2% from the 1970s to the 1990s, and 21.0%-37.6% from the 1990s to the 2000s). The impact of climatic conditions on maize yield has exhibited an increasing trend (0.67%-22.5% from the 1950s to the 1970s, 2.6%-27.0% from the 1970s to the 1990s, and 9.1%-51.1% from the 1990s to the 2000s); however, interannual differences can be large, especially if there were large changes in temperature and rainfall. Among climatic factors, rainfall had a greater positive influence than light and temperature on yield increase. Cultivation measures could change the contribution rates of variety and climatic conditions. Overall, unless there is a major breakthrough in variety, improving cultivation measures will remain important for increasing future summer maize yields in the Huanghuaihai region.