【Objective】This research aims to study the effect of photosynthesis, nitrogen metabolism key enzyme activities and other related indexes of poplar main planting varieties under different water and fertilizer management, and to provide a theoretical basis for the construction of efficient and precise water and fertilizer management system of poplar plantations, especially for the cultivation of large diameter timber.【Method】Taking the 11-year-old Populus × euramericana ‘Neva’ plantation in the sandy area of north China as the research object. Seven water and fertilizer management treatments were set up: conventional furrow irrigation (CK), drip irrigation (ND), controlled-release fertilizer + drip irrigation (CD), and water-soluble fertilizer + drip irrigation (M1D, M2D), formula fertilizer + drip irrigation (F1D, F2D). During the growing season (July to September), continuous monitoring was performed to assess key physiological and biochemical indices associated with photosynthesis and nitrogen metabolism in poplar leaves across the different treatments. Subsequently, we analyzed and compared the physiological and biochemical responses of the plantation under varying management regimes. Finally, a comprehensive evaluation of the effects of different water and fertilizer strategies was conducted using subordinate function analysis.【Result】Different water and fertilizer management on nitrogen metabolism (nitrate reductase (NR), glutamate synthase (GOGAT), Glutamate dehydrogenase (GDH)), photosynthesis (ribulose-1,5-diphosphate carboxylase/oxygenase (Rubisco), fructose-1,6-bisphosphate phosphatase (FBA)) key enzyme activities, soluble sugar (SS) and chlorophyll (Chl) content were significantly affected (P < 0.05), and the values of each index showed a continuous increasing trend with month, and the interaction between month and treatment was highly significant (P < 0.01). Under all water and fertilizer management, the overall trend of each index showed continuous increase with increasing months and reached the maximum value of each index in September. NR, GOGAT, GDH, Rubisco, FBA activity and SS content were increased under ND treatment compared to CK, but the overall difference was not significant; compared with ND these physiological and biochemical indexes were significantly increased by 13.60%-188.56% under different water-fertilizer-coupled management (CD, M1D, M2D, F1D, F2D); compared with CD, drip fertigation (M1D, M2D, F1D, F2D) significantly increased the activities of key enzymes of photosynthesis and nitrogen metabolism and the SS content by 11.22%-68.78%. The Chl content was significantly increased mainly in F1D and F2D in August and September, and was significantly increased by 31.29%-123.55% over M1D and M2D. The analysis of the subordinate function analysis showed that the F2D treatment had the greatest effect on the physiological and biochemical indexes of poplar, followed by F1D and M2D.【Conclusion】Different water and fertilizer management can significantly affect the physiological and biochemical indexes of photosynthesis and nitrogen metabolism enzyme activities in poplar plantation, among which the drip fertigation measures have the greatest impact, significantly higher than other measures, and the addition of medium and trace elements helps to significantly increase the chlorophyll content. Drip fertigation measures were adopted, in which the annual fertilizer ratios were N(520 g per tree), P₂O₅(169 g per tree) K₂O(312 g per tree), and the annual addition of 5 g per tree of trace elements (including Fe, Ca, Mn and Zn) had the greatest impact on the physiological and biochemical characteristics of poplar plantation. The results provide theoretical and technical references for the construction of a precise water and fertilizer management system for efficient cultivation of poplar plantation in sandy areas of north China and similar ecological conditions, especially for large diameter timber.