Context: Water-efficient and high-yield agricultural practices are critical for achieving sustainable development, particularly in semi-arid regions like Northwest China where winter wheat production faces severe water scarcity. As irrigation and plant density are two closely linked management factors, understanding their effects on photosynthetic traits and chlorophyll fluorescence is essential for optimizing resource use and ensuring yield stability. Methods: A two-year field experiment was conducted using three plant density levels (PD1: 562.5 x 10' plants ha-1; PD2: 375 x 10' plants ha-1 and PD3: 187.5 x 10' plants ha-1) in combination with four irrigation strategies (I0: rainfed; I1: pre-winter + jointing; I2: jointing only and I3: jointing + anthesis stage). Results: Across both growing seasons the PD3-I2 treatment (low plant density, jointing-only irrigation) yielded the highest net photosynthetic parameters at anthesis. Compared to PD1-I2, the PD3-I2 significantly increased the net photosynthetic rate (by 11.75 % and 11.02 %), transpiration rate (by 15.20 % and 8.71 %), stomatal conductance (by 13.22 % and 20.59 %), and intracellular COQ concentration (by 2.42 % and 7.17 %). Irrigation at jointing (I2) consistently enhanced the effective yield of Phi PSII by 3.36-3.84 % across all plant density levels. The PD3-I2 combination was particularly effective, significantly increasing photochemical quenching (qP) by 5.87-15.51 % and PSII vitality index (Fv/Fo) by 4.14-7.67 % over the PD1-I2 treatment. The grain-yield-optimizing combination varied interannually: maximum grain yield was achieved under PD3-I2 in 2022-23 (5819 kg ha-1) and PD2-I2 in 2023-24 (6310 kg ha-1). Notably, irrigation at the jointing stage increased the yield by upto 18 % in medium and low plant density (PD2, PD3) compared to the other regimes, demonstrating that I2 was most effective when not combined with higher PD. Mantel's test revealed significant correlations among management practices, key physiological traits and grain yield, though these relationships were modulated by inter-annual climatic variability. Conclusions: This study demonstrated that a combination of lower plant density (187.5-375 x 10' plants ha-1) with supplemental irrigation at the jointing stage optimizes photosynthetic performance and enhances grain yield stability in winter wheat under semi-arid conditions. These findings advocate for a strategic approach: using limited water resources to establish and support an optimal plant population structure, thereby reconciling the trade-off between water conservation and yield enhancement. This integrated management practice is recommended as a climate-resilient strategy for sustainable wheat production in arid and semi-arid regions.