Abstract: To clarify the differences in light energy utilization and distribution characteristics of flag leaf ¹³C assimilate in different spike-type wheat varieties and their responses to supplementary irrigation, we set three water treatments in a field experiment, including no irrigation during growth duration of wheat (W₀), water-saving irrigation (W₁, irrigating at jointing and anthesis of wheat to keep the relative moisture of 0-40 cm soil to 65% and 70%), full irrigation (W₂, irrigating at jointing and anthesis of wheat to keep the relative moisture of 0-40 cm soil to 85% and 90%) with the medium-spike wheat cultivars Jimai 22 and Qingnong 2, large-spike wheat cultivars Shannong 23 and Shannong 30 as test materials. The effects of different water treatments on canopy light energy utilization and ¹³C assimilate distribution characteristics of two spike-type wheat varieties were examined. The results showed that leaf area index, canopy light interception rate, and light energy utilization rate of the two varieties at 2, 11, 20 and 31 days after anthesis were significantly higher than W₀ treatment, but there was no significant change in each index when the irrigation increased to W₂ treatment. The distribution of flag leaf ¹³C assimilates of Jimai 22 and Shannong 23 of W₁ in grain was 159.34 and 171.1 g·hm^-2 higher than W₀, respectively, and the distribution ratio was 6.5% and 6.5%, with no significant difference compared with W₂. The grain yields of both varieties under W₁ were significantly higher than that under W₀, but with no significant difference with W₂. Under water-saving irrigation, the medium-spike cultivars had higher canopy photosynthetically active radiation interception and utilization ability at 2 and 11 days after anthesis and large-spike cultivars at 20 and 31 days after anthesis. The distribution amount and ratio of ¹³C assimilates in the grain of medium-spike variety Jimai 22 flag leaf were 6.8% and 2.7% lower than that of the large-spike variety Shannong 23.