Abstract: 【Objective】This study on the effects of different nitrogen application rates on the photosynthetic characteristics and yields of oil tree peony(Paeonia ostii‘Feng Dan')was conducted to determine the reasonable nitrogen fertilizer application, which could provide atheoretical basis for high-yield cultivation. 【Method】The control(N₀)and seven nitrogen fertilizer rates, including 150(N₁), 225(N₂), 300(N₃), 375(N₄), 450(N₅), 525(N₆), and 600(N₇)kg/hm², were used, and the responses of the parameters of photosynthesis and the yield of ‘Feng Dan' at the flowering stage relative to different nitrogen application rates were analyzed.【Result】Compared with the control, the parameters of photosynthesis and grain yield were significantly improved under each nitrogen treatment, and the difference among N application rates was significant(P<0.05). The net photosynthetic rate, stomatal conductance, and transpiration rate of the leaves increased to their highest levels at the level of N₅, which resulted in increases of 37.47%, 70.06% and 32.83%, respectively; and the intercellular CO₂ concentration decreased by 11.43%, relative to that of the control.In addition, 1 000-grain weight(318.58 g)and seed yield per plant(41.58 g)were significantly higher than those in other nitrogen treatments(P<0.05), and increased by 26.17% and 282.16% compared with that of the control, respectively.【Conclusion】The photosynthetic characteristics and yields of Paeonia ostii ‘Feng Dan' were significantly improved at the level of N₅(450 kg/hm²)in this study, which could be recommended as a reasonable nitrogen application rate.