Abstract Close planting often increases the lodging rate of maize, but the cause is unclear. Close planting reduces light intensity within the canopy; therefore, we hypothesized that light intensity may be the main factor affecting maize lodging. To test this hypothesis, three field experiments involving plant density, shading and defoliation were designed to explore how the light environment in a maize canopy affects stalk strength formation and lodging rate. The results showed that close planting and artificial shading treatments both reduced light intensity in the lower canopy. This reduced the dry weight per unit length (DWUL) and rind penetration strength (RPS) of the third basal internode and increased the lodging rate. Removal of leaves 10–12 reduced the DWUL and RPS of the third internode and increased lodging rate. This showed that leaves 10–12 play a crucial role both in the formation of RPS of the third basal internode and in lodging resistance. Removal of either all or part of leaf 16 and above not only increased ptotosynthetic active radiation (PAR) at leaves 10–12 but also increased the DWUL and RPS of the third basal internode. This resulted in a decline in lodging. Therefore, we conclude that light intensity is an important factor affecting maize lodging at high plant density. Increasing light intensity at leaves 10–12 can enhance stalk strength and reduce lodging.