Effects of planting densities and modes on developmental characteristics of summer maize populations were studied in two varieties (Zhengdan 958 and Xundan 20) under high yield condition in Northern Henan Province. The results showed that plant height, stem diameter, height of ear position, leaf area index, chlorophyll content in leaves, biomass of shoots, characteristics of ear, grain yield and harvesting index were significantly influenced by planting density and mode. The yield of Zhengdan 958 was the highest (14236.97 kg/hm2) at a density of 90000 plants per hm2 in wide\|narrow row planting mode, while the yield of Xundan 20 was the highest (13333.51 kg/hm2) at a density of 82500 plants per hm2 in wide\|narrow row planting mode.