Abstract: 【Objective】 The effects of different nitrogen forms and their proportion on phenotypic traits, photosynthetic characteristics, and grain yield of Paeonia ostii ‘Feng Dan’ were studied to determine the optimal proportion of nitrogen forms and promote high-yield and high-efficiency scientific fertilization. 【Method】 Three different nitrogen forms, ammonium nitrogen(NH⁺₄-N), nitrate nitrogen(NO^-₃-N), and amide nitrogen(N-CONH₂), were used to set different nitrogen forms and their proportions. Phenotypic traits, photosynthetic characteristics and yield traits were investigated. 【Result】 Compared with the control, different forms of nitrogen fertilizer and ammonium nitrate combination had significant effects on phenotypic traits, photosynthetic characteristics, and grain yield parameters of P. ostii ‘Feng Dan’ under conditions of fixed phosphorus and potassium fertilization(P<0.05). Net photosynthetic rate, stomatal conductance, and transpiration rate of P. ostii ‘Feng Dan’ leaves were the highest under treatment with ammonium nitrogen and nitrate nitrogen at a 50:50 proportion, which increased by 22.85%, 39.18% and 25.98%, respectively; the intercellular CO₂ concentration was 14.67% lower than the control; the 1 000-grain mass and the yield per individual were the highest, and significantly higher than under other fertilization treatments(P<0.05), and were 31.86% and 43.05% higher than the control. 【Conclusion】 The combination of ammonium and nitrate can greatly improve phenotypic traits, photosynthetic characteristics, and yield of P. ostii ‘Feng Dan’, providing a theoretical basis for the rational fertilization of P. ostii ‘Feng Dan’.