In order to investigate high densities and planting methods of summer maize in north China, in 2010-2011, two varieties (Ludan 981, LD981, and Ludan 818, LD818) were selected and planted in two densities (6 0000 and 90000 plants/hm²) at two planting methods (single and double plants at one place). In this experiment, eight treatments were designed to study the effect of planting methods on root-shoot development and grain yield of summer maize under high densities. The results showed that vertical distribution of canopy resulted in a trend that dry matter weight increased with planting density increased; however, root vertical distribution resulted in a opposite trend. Under high density conditions,there were different competitive ability of root and shoot between different maize varieties. The canopy of LD981 was more sensitive to space, and its space competition of root was stronger than that of the canopy, hence, the yield limiting factor of LD981 was the kernel storage capacity; however, the root of LD818 was more sensitive to space, and its space competition of canopy was stronger than that of the root, hence, the yield limiting factor of LD818 was the spike number per unit. Under the condition of 60000 plants/hm², the quality of canopy structure and function of LD981 was better, double plants at one place reduced competitive stress in the canopy, as a result, achieved root and shoot equilibrium. Hence, the population yield enhanced; under the condition of 90000 plants/hm², the quality of canopy structure and function of LD818 was better, double plants at one place alleviated root competition, the quality of canopy structure and function improved partly, therefore, the root and shoot coordinated, which let to the yield increased.