In order to clarify the effects of water deficit and rehydration on the assimilation transport and grain filling of wheat after anthesis, we applined three treatments, named, well water (WW), rehydration after moderate drought stress (MD) and rehydration after severe drought stress (SD), after 9 days flowering in pot experiment with wheat cultivar ‘Changhan 58’. The yield, grain filling dynamics, photosynthetic performance of flag leaves, nonstructural carbohydrate (NSC) transport in stem and sheath and the activities of key enzymes in grain, were investigated during the process of drought and rehydration. The results showed that: (1) compared with WW treatment, MD significantly increased the number of grains per spike and thousandgrain weight of wheat and thus improving the grain yield, water use efficiency and maximum grouting rate of grains and the average filling rate. For the SD treatment, grain numbers per spike, the superior and inferior spikelets of maximum grouting rate and the average filling rate were significantly decreased, but the water use efficiency was significantly increased compared with WW. (2) The photosynthetic rate of flag leaves during wheat filling had no difference between MD treatment and WW treatment. Meanwhile, compared with WW, stomatal conductance and transpiration rate at 9-20 d after wheat flowering were not changed under MD, while they were profoundly decreased under SD. (3) The activities of sucrose synthase and adenosine diphosphate glucose pyrophosphorylase in wheat was increased by MD treatment; Meanwhile, MD had lower fructose content, which suggested that contribution of substances in stem to the yield were increased. The study found that higher photosynthesis, more assimilates in the stem after anthesis transfer to the grain and higher sugar metabolism enzyme activity in the inferior spikelets, and the number of grains per spike and thousandgrain weight, then finally increase the physiological basis of yield.