Abstract: A pot experiment and paraffin sections were used to determine the development and micro-structures of ear vascular bundle system of two wheat (Triticum aestivum L.) genotypes at the late growth stage under water deficit. The relationships between ear vascular micro-structures and carbon assimilate stagnation were also analyzed. The study shows a fan-shaped distribution of the newly formed vascular bundles near the rachis of “Pubing143” and “Xinong979” during anthesis. Away from the rachis is ellipse or other forms of distribution under normal and water-deficit conditions. The cells between the new and original vascular tissues increase to eventually form sclerenchyma. With the development of ear, some of the original and new vascular tissues spread out to the glume and rachilla. The branches afterwards spread out to the lemma, lodicule and palea of the first and subsequent flowers. The parameters of vascular bundle system (such as the number and area of large and small vascular bundles) from base to top of ear decreases under water deficit condition. This may be one of the reasons of carbon assimilate stagnation in the gulme and rachis. Spike grain weight declines and non-grain organ biomass increases significantly in the two wheat genotypes under water deficit condition. This is more obvious for “Pubing143”, genotype for rainfed areas.