Abstract: Lodging is a crucial factor affecting the high and stable yield of summer maize. To study the effects of different stages and types of lodging on 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 (light root lodging EQ, severe root lodging EZ, and stem bending EJ). Using the Logistics curve to simulate the dynamics of grain filling, the study analyzed changes in the duration and rate of grain filling during the rapid increase phase T1, the gradual increase phase T2, and the slow increase phase T3, and quantitatively assessed the yield loss due to different lodging treatments. The results showed that the Logistics simulation, with a determination coefficient of over 0.98, fitted the grain filling dynamics of summer maize well. Post-lodging, significant reductions in the theoretical maximum 100-grain weight (K value) were observed in 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 the E3 stage, and by 6.0%−16.0% (EZ) and 14.9%−18.8% (EJ) during the E4 stage. Excluding the E1 stage, average grain filling rate G_avg, maximum grain filling rate G_max, and the grain mass at maximum filling rate W_max were significantly impacted, with average filling rates of ‘Zhengdan 1002’ declining less than those of ‘Yudan 9553’. Specifically, 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 (T1, T2, and T3) under lodging treatments at different stages were not significantly different from the control, but a clear decline in filling rate was evident, particularly during the rapid increase phase T2 and the slow increase phase T3. Post-lodging, grain filling rates G2 and G3 significantly declined in the E1 stage after stem bending EJ, and in the E2, E3, and E4 stages after stem bending EJ and severe root lodging 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’), where stem bending lodging resulted in the highest yield reduction, followed by severe root lodging. 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 ‘Yudan 9553’.