Abstract: Taking different genotype cotton varieties as test materials, a soil column culture experiment was conducted to study the effects of water and nitrogen management modes on the photosynthetic characters and yield formation of cotton with undermulch drip irrigation in Xinjiang, Northwest China. Under the management mode W₄N₂, i.e., pre-sowing irrigation + limited drip irrigation before full-flowering + abundant drip irrigation after fullflowering in combining with basal 20% N + topdressing 80% N, the chlorophyll content, net photosynthetic rate (P_n), stomatal conductance (g_s), actual photochemical efficiency of photosystemⅡ (Φ_PSⅡ), and photochemical quenching coefficient (q_P) at full-flowering stage all decreased significantly, the non-photochemical quenching (NPQ) increased, and the aboveground dry matter accumulation was inhibited, as compared with those under common drip irrigation. From fullflowering stage to bollopening stage, the chlorophyll content, g_s, P_n, Φ_PSⅡ, and q_P increased with increasing water and nitrogen supply, and the aboveground dry matter accumulation was enhanced by compensation, which benefited the translocation and distribution of photosynthates to seed cotton. Under the fertilization mode of basal 20% N + topdressing 80% N, the seed cotton yield of Xinluzao13 was the highest in treatment pre-sowing irrigation + common drip irrigation (W₃), but that of Xinluzao43 was the highest in treatment pre-sowing irrigation + limited drip irrigation before full-flowering + abundant drip irrigation after full-flowering (W₄). It was concluded that under the condition of pre-sowing irrigation, to appropriately decrease the water and nitrogen supply before full-flowering stage and increase the water and nitrogen supply at middle and late growth stages could extend the active photosynthesis duration and promote the photosynthates allocation to reproductive organ, which would fully exploit the yield-increasing potential of cotton with under-mulch drip irrigation.