Abstract: Experiments were made to study the physiological changes of wheat plants during grain development in different temperatures. The results obtained are summarized as follows: 1. When wheat plants were cultured at the same day temperature (25℃) and different night temperatures (10℃, 20℃) from flowering to ripening, the period of grain-filling was prolonged for 10 days by low night temperature treatment. 2. Under low night temperature condition, the area of green leaves increased, the senescence of the lower leaves was retarded, the respiratory activities of leaves were lower in the night. All the responses mentioned above favored the accumulation of dry weight of the plant. Although stems, leaf sheaths, spikes and grains increased on dry weight respectively, yet the accumulation of dry matters was mainly due to the growth of stem from the beginning of flowering to 17th day after flowering. In ripening stage the difference of the dry weight of grains between high and low night temperature treatments increased significantly. 3. Since the photosynthetic products were rich in the low night temperature treatment, it favoured the growth of late flowered grains. Therefore, low night temperature treatment not only increased the weight of the 1st and 2nd grains, the fertility and the weight of 3rd grains also increased. 4. The soluble sugar content of leaf sheaths, leaves, especially the stem was higher in low night temperature treatment than in high night temperature treatment. During early stage of grain development, the alcohol soluble sugar content of grains was high and the starch content low in the low night temperature treatment. The difference between the two treatments became insignificant as plant grew to ripening. 5. In the milk ripe stage the translocation and distribution of C14-assimilated products were changed by local temperature variation (from 5–8 ℃ to 20–25 ℃) around the spike, the internode below spike or the feeding leaf. The photosynthetic products translocated to grains was inhibited by low temperature treatment. The effect of inhibition was greater when the low temperature treatment was around the spike than when the treatment was around the feeding leaf. Treatment of low temperature around the node below spike gave weak effect. 6. The increase of alcohol soluble substances of either supplying, conductive or receiving organ was reduced by low temperature treatment, and the spikes was most sensitive to low temperature. The radiactive activity of alcohol soluble part in the grains was about 65% in the low temperature treatment around the spike, but in the untreated plant about 63% of radiactive activity in the grains was in the dilute acid part. It was indicated that the processes of the transformation of sugars to high molecular substances in the grains was inhibited. 7. The physiological considerations of high thousand grain weight in Chinhai province, the effects of night temperature on the growth of grains, and the possibility to increase grain weight per spike are discussed.