Abstract:The optimum planting density is needed to achieve maximum crop yield. The effect of planting density on grain yield, agronomic and physiological traits of winter wheat cultivar Linkang No.2 was studied under the northwest oasis condition of China. Six seeding rates from 225 to 450 kg hm2 （275 to 516 plants•m-2） were evaluated. Significant differences in grain yield, spike number per unit area, kernels per spike, kernel weight, water use efficiency(WUE), spikes per plant, stems per plant, leaf area index (LAI), plant height, photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs) and the canopy apparent photosynthesis rate (CAP) were found among the density treatments. The highest grain yield (8650 kg hm2) was obtained with the planting density of 390 plants•m-2. Grain yield was highly correlated with spike number per unit area (r=0.89**), but not with kernels per spike and kernel weight. The grain yield in this experiment was not affected by Pn, Gs and Tr of the single leaf measured on five occasions throughout the growing period. However, a significant correlation was found between yield and LAI at the early and middle grain fill, and with CAP at anthesis. The change in Pn, Tr or Gs for the growth period for all planting densities was bimodal with peaks at heading and early grain fill. The highest value of Pn appeared at heading, but those of Tr and Gs appeared at early grain fill. Although highly positive correlations were observed between the means of Pn, Tr and Gs across the five times of measurement (r=0.94** to 0.97**), their correlations at different growth stage still showed considerable differences (r=0.53 to 0.99**). Pn, Gs and Tr for the single leaf showed were not significantly correlated with CAP.