Abstract: Densification planting and delayed harvesting are important measures for the promotion and development of mechanized grain harvesting technology of maize, but they also reduce the lodging resistance of stalks and increase the risk of lodging. The appearance of maize lodging not only increases the difficulty of mechanical harvesting and reduces the speed of mechanical harvesting, but also increases the loss of ear caused by lodging and reduces the yield of mechanical grain harvest. Therefore, the purpose of this experiment was to explore the changing law of the lodging resistance ability of maize stalks after physiological maturity under different densities and to provide a scientific basis for the development of maize dense planting and high-yielding mechanical grain harvest technology. This experiment used ‘Zhenghong 6’ as the material and set 6 density treatments: 3.0×10⁴ plants∙hm⁻² (B1), 4.5×10⁴ plants∙hm⁻² (B2), 6.0×10⁴ plants∙hm⁻² (B3), 7.5×10⁴ plants∙hm⁻² (B4), 9.0×10⁴ plants∙hm⁻² (B5), and 10.5×10⁴ plants∙hm⁻² (B6). In the physiological maturity period (August 6, A1), 11 d after physiological maturity (August 17, A2), 22 d after physiological maturity (August 28, A3), and 35 d after physiological maturity (September 10, A4), 5 plants in each plot were sampled and the changing laws of stalk strength, internode morphology, internode dry matter, moisture content, etc. were determined. The results showed that the internode stalk strength of maize decreased after physiological maturity, but the decreasing range gradually reduced with time. After physiological maturity, the dry weight per unit length and water content of stalk decreased, while the internode length-to-diameter ratio increased slightly. Stalk strength and it’s change with time were significantly different among different densities after physiological maturation. In the density range of 4.5×10⁴ plants∙hm⁻² to 10.5×10⁴ plants∙hm⁻², the decreased amplitude of stalk strength showed a decreasing trend with the increase of density, and that of stalk strength of low density was greater than that of high density. The increase in planting density resulted in a significant decrease in stalk dry weight per unit length and a significant increase in the internode length-to-diameter ratio. The results showed that the decrease of stalk dry weight per unit length after physiological maturity was the main reason for the decrease of stalk strength. The increase of planting density significantly reduced the stalk strength, and with the extension of standing time, the stalk strength further decreased. The stalk strength of different densities decreased differently, and the decrease rate of low density was greater, but the stalk strength of high density was still lower than that of low density treatment all the time. Therefore, properly dense planting and harvest at the right time can reduce the risk of lodging caused by the decline of the standing capacity of culms after physiological maturity of maize.