Abstract: Lodging is a crucial factor affecting the yield of summer maize. To study the effects of different stages and types of lodging on the grain filling and yield of summer maize, this study selected two varieties, “Zhengdan 1002” (sparsely planted with large ears) and ‘Yudan 9553’ (densely planted with small ears), and conducted a field control experiment at four key growth stages (E1: large trumpet mouth stage, E2: flowering stage, E3: grain formation stage, and E4: mid-grain filling stage) with three types of lodging (EQ: light root lodging, EZ: severe root lodging, and EJ: stem bending). Using a logistic curve to simulate the dynamics of grain filling, this study analyzed changes in the duration and rate of grain filling during the gradual increase phase, rapid increase phase, and slow increase phase and quantitatively assessed the yield loss due to different lodging treatments. The logistic simulation fit the grain-filling dynamics of summer maize well, with a determination coefficient of over 0.98. Post-lodging, significant reductions in the theoretical maximum 100-grain weight (K value) were observed at E3 and E4 stages, with ‘Zhengdan 1002’ experiencing greater reductions than ‘Yudan 9553’. In particular, K values significantly decreased by 8.8%–16.5% (EZ) and 15.4%–22.3% (EJ) during E3 and 6.0%−16.0% (EZ) and 14.9%−18.8% (EJ) during E4. Excluding the E1 stage, the average grain filling rate G_avg, maximum grain filling rate G_max, and grain mass at maximum filling rate W_max were significantly affected, with average filling rates of ‘Zhengdan 1002’ decreasing less than those of ‘Yudan 9553’. Specifically, the average filling rates decreased by 10.5%–11.8% (EZ) and 12.4%–14.6% (EJ) during E2, 18.0%–18.1% (EZ) and 17.6%–21.2% (EJ) during E3, and 13.6%–16.6% (EZ) and 14.1%–23.0% (EJ) during E4. The durations of the three grain-filling phases under lodging treatments at different stages were not significantly different from those of the control but a decline in the filling rate was evident, particularly during the rapid and slow increase phase. Post-lodging, grain filling rates during the rapid and slow increase phase significantly decreased in the E1 stage after EJ and in the E2, E3, and E4 stages after EJ and EZ. Light root lodging had no significant impact on grain-filling rates. Analysis of post-lodging yield changes showed that the E2, E3, and E4 stages had a greater impact on yield, with average reductions of 18.2%−21.1% (‘Zhengdan 1002’) and 21.1%−24.0% (‘Yudan 9553’), whereas EJ resulted in the highest yield reduction, followed by EZ. Lodging had a greater impact on ‘Yudan 9553’ than on ‘Zhengdan 1002’. In summary, lodging during the middle and late stages of summer maize growth significantly reduces the grain-filling rate and mainly affects the filling rate during the rapid and slow growth periods. Lodging significantly reduces yield, especially for densely planted spikelet-type varieties, such as ‘Yudan 9553’.