Abstract: This study, conducted to provide a theoretical basis for suitable sowing dates for the high yield and high-efficiency cultivation of maize in the Chengdu Plain, explored the relationships between 100-kernel weight (KW), grain filling parameters, and sowing date-associated meteorological factors after silking. To investigate the dry matter accumulation and grain filling characteristics under different sowing dates, the widely adaptive maize cultivar ‘Zhongyu 3’ was sown on six dates (March 27, April 6, April 16, April 26, May 6, and May 16). The results showed that with delayed sowing dates, the growth period of maize decreased, and grain yield and KW decreased significantly. The decreased yield was mainly attributed to KW, and variations in the grain-filling rate (G_mean) and the kernel weight at the maximum grain-filling rate (W_max) were the primary factors that influenced KW. Both G_mean and W_max were markedly affected by the effective accumulated temperature (AT), daily average temperature (MT), and precipitation (P_r) after silking. In this experiment, G_mean, W_max, and final KW increased along with MT and AT. A large amount of precipitation occurred during the grain filling period owing to the delayed sowing dates resulted in a decrease in G_mean and KW. AT was the major factor influencing grain-filling characteristics and KW, and a relatively prolonged growth period under early sowing conditions contributed to the increased effective accumulated temperature after silking, which was beneficial for grain filling. With sowing on April 6, higher KW and maize yield were obtained with better grain-filling performance when the effective accumulated temperature reached 863.36 °C. We concluded that suitable sowing dates should be established for the different planting systems used in maize cultivation. Spring maize should be sown as early as possible in the plain regions of the Sichuan Basin from the end of March to the beginning of April. The relationship with the previous crop should be considered in summer sowing especially for areas where late sowing is unavoidable, with sowing being completed in early May to avoid the adverse effects of abnormal meteorological factors on grain filling.