Matching of maize growth with solar radiation is of great importance for achieving high yield. We conducted experiments using different maize cultivars and planting densities under different solar radiations during grain filling to quantitatively analyze the relationships among these factors. We found that a decrease in solar radiation after silking caused a drop in maize grain yield and biomass, with lower solar radiation intensities leading to worse grain yields and biomass. Cultivar ZD958 was more sensitive to solar radiation changes than cultivar XY335; slight decreases in solar radiation (i.e., 15% shading) caused significant declines in ZD958 grain yield. When total solar radiation during grain filling was less than 486.9 MJ m-2 for XY335 and less than 510.9 MJ m-2 for ZD958, the two cultivars demonstrated high yields at lower planting density of 7.5 × 104 plants ha-1; average yields were 13.36 and 11.09 Mg ha-1, respectively. When radiation intensities were higher than 549.5 MJ m-2 for XY335 and higher than 605.8 MJ m-2 for ZD958, yields were higher at a higher planting density of 12 × 104 plants ha-1, with average yields of 20.58 Mg ha-1 for XY335 and 19.65 Mg ha-1 for ZD958.