In order to study the effects of high temperature on grain development and crystal properties of wheat (Triticum aestivum L.), we selected the main varieties of XC11 and XC39 with different qualities and maturity stages. They were treated at the early (T₁) and middle (T₂) stage after anthesis under high temperature, respectively. The results showed that: (1) T₁ treatment significantly reduced grain length and grain weight of two varieties, while T₂ treatment had greater effects on grain width and thickness. Although the grain filling rate was decreased by high temperature treatment, the maximum peak time of the two varieties appeared at 18 day after anthesis (DAA). (2) For morphology of starch grains, the influence on the Atype starch granules morphology is more serious under high temperature treatment. Under T₁ treatment, pores of Atype starch granule of XC11 can be observed in surface at 10 DAA, Atype starch granule size significantly less than the same period controlled starch granule size at 15-20 DAA, starch granule surface indentation increased at 20-25 DAA and A and Btype starch granule surface significantly constricted. However, the shape and size of starch granule of early maturing XC39 were less affected by the high temperature after anthesis. (3) Under different high temperature treatments, the diffraction peaks of starch grains were the same, but the peak intensities of starch grains were different between the two varieties. The results showed that high temperature stress did not affect the crystal type of starch grains, but changed the lamellar structure of starch grains. The early high temperature after anthesis not only has a great influence on the grain morphology, but also affects the morphology and crystal characteristics of starch grains in the grains.