Abstract: Abstract：Study the change of grain filling rate of Jingdan68 and Zhengdan958 under different sowing dates. Jingdan68 and Zhengdan958 with two sowing dates (14 May, and 13 June) were used in field experiments. The average temperature, maximum and minimum temperature, accumulated temperature during the grain filling stage under spring sowing were 1.22 ℃, 0.54 ℃ and 2.37 ℃, 480.54 ℃ higher than the summer sowing condition. Under spring sowing condition, the 100-grain dry weight of Jingdan68 and Zhengdan958 was 43.03 g and 39.02 g, and 41.17 g and 34.80 g under summer sowing condition; The dry weight of 100-grain at maximum grain filling rate (Wmax), the thermal time needed during the active grain filling period (P) under spring sowing were higher than that of summer sowing condition. Thus, the maximum grain filling rate (Gmax), initial grain filling potential (Ro), the thermal time reaching the maximum filling rate (TGDD) showed opposite trend. The TGDD and P of Zhengdan958 were higher than Jingdan68, but the Wmax, Gmax, Ro performance opposite trend. The study showed that grain filling of Jingdan68 was started as early as Zhengdan958, initial grain filling potential and grain filling rate were higher than Zhengdan958 and the accumulated temperature required for its active grain-filling period was less than Zhengdan958, so final grain dry matter weight significantly higher than Zhengdan958.