Plant density significantly affects grain yield and dry matter accumulation in summer maize cultivar Denghai 661. Higher plant density leads to increased yield and dry matter accumulation per hectare, but decreased per plant. Denghai 661 shows optimal growth potential at 90,000 plants per hectare for maximum yield. Stem dry matter accumulation decreases more than leaf before milking stage, but the opposite is true after milking stage. Stem contributes more to grain yield at lower densities, while leaf contributes more at higher densities.