Abstract: 【Objective】The objective of this study was to explore the impact of fertilizer application depth on the photosynthetic characteristics and yield formation of flag leaves in spring wheat,aiming to offer a theoretical basis for the deep fertilization of dryland spring wheat.【Method】A pot experiment was conducted using Longchun 35 spring wheat,implementing four treatments:wet chemical fertilizer applied shallowly at 15 cm (W₁₅),wet chemical fertilizer applied deeply at 30 cm (W₃₀),dry chemical fertilizer applied shallowly at 15 cm (D₁₅),and dry chemical fertilizer applied deeply at 30 cm (D₃₀).The SPAD value,leaf area,photosynthetic parameters,dry matter accumulation,filling rate,and yield of spring wheat flag leaves were assessed.【Result】Deep fertilizer application (W₃₀,D₃₀) notably enhanced the leaf area,dry matter accumulation,filling rate,and SPAD value of flag leaves in dryland spring wheat.It facilitated the transfer of assimilated dry matter to seeds.At the flag picking stage,the SPAD values of flag leaves increased by3.1%and 5.8%in the deep fertilizer treatments (W₃₀ and D₃₀) compared to the shallow fertilizer treatments (W₁₅ and D₁₅).The leaf area of flag leaves increased by 19.5%and 23.7%,respectively.Moreover,the average filling rate from 20 days to 40 days after flowering increased by 7.0%and 6.7%,respectively,and the dry matter accumulation per plant at maturity increased by 12.9%and 11.1%,respectively.Photosynthetic parameters P_n,G_s,and T_r were significantly higher with 30 cm fertilizer depth compared to 15 cm depth,while C_i showed the opposite trend,particularly pronounced under drought conditions.Thousand grain weight and grain number increased by 14.0%,7.7%,and 3.8%,9.3%,respectively,with deeper fertilization (W₃₀,D₃₀) compared to shallower fertilization (W₁₅,D₁₅),resulting in a yield increase of 13.0%and 16.0%.【Conclusion】Deep fertilization can mitigate water deficits,enhance photosynthesis and grain filling in spring wheat,and sustain high economic and biological yields.This approach may be recommended for adoption in dry spring wheat cultivation in the northwest Loess Plateau.