Abstract: The main mode of resource assimilation relevant to wheat grain yield is photosynthesis. Irrigation is a critical cultivation measure for plant growth and photosynthesis. Despite the tremendous progress in understanding the effects of irrigation on photosynthesis, the mechanism of irrigation on population photosynthesis (PP) remains unclear. A field experiment was therefore conducted to clarify the regulation mechanisms of different irrigation schedules on population photosynthetic of winter wheat. The experiment included 5 irrigation schedules no irrigation (W0), 1-time irrigation at jointing (W1j) or booting (W1b) stage, 2-time irrigation at jointing and booting stages (W2), and 3-time irrigation at jointing, booting and grain-filling stages (W3) and 3 planting densities 180 (D1), 300 (D2) and 450 (D3) seedlings per square meter. The results indicated that irrigation significantly improved PP. The relationship between PP and irrigation time/volume was to some extent parabolic. Improvements in PP (resulting from more irrigation time/volume) were mainly related to increases in leaf area index (LAI) and population light interception. PP exhibited a significantly negative correlation with percent canopy light transmittance. PP at grain filling stage was significantly positively correlated with accumulated dry matter and grain yield. In terms of main effects, partial correlation analysis showed that PP of W0, W1j, W1b and W3 was regulated by percent population light transmission and leaf area. On the other hand, W2 PP was mainly influenced by flag-leaf photosynthetic rate. This indicated that spring irrigations at jointing and booting stages (W2) led to higher photosynthetic rate and yield output. On this basis, planting 300 seedlings per square meter was the optimum combination. The combination of W2 and D2 increased PP during mid-late growth stages and extended high PP duration, which ultimately increased grain yield.