Abstract: Through fertilizer effect field trials, the study aims at testing the effect of root fertilizing with nitrogen (N), phosphorus (P) and potassium (K) on the net photosynthetic rate (Pn) of J. regia‘Wen185’under the medium soil nutrient condition, and provide a theoretical basis for scientific fertilization and management in walnut orchards. Both“3414”fertilizer effect field trial and the multiple linear stepwise regression analysis were used. The results showed that the denary logarithm (log10M) of the daily mean value (M) of the net photosynthetic rate of J. regia‘Wen185’had a highly significant linear correlation (P＜0.001) with the fertilizing amount of N fertilizer (pure amount of N) and its square (N×N or N2), the linear relationship was log10 M? =0.724 0.231N-0.084N2 0.153P2. There was a positive effect of N fertilizer on the net photosynthetic rate of J. regia‘Wen185’under the medium soil nutrient condition (available P 14.0 mg/kg, available K 77 mg/kg) in walnut orchards when the fertilizing amount of N fertilizer (pure N amount) was less than 2.75 kg per tree; otherwise the effect was negative. Meanwhile, the application of P fertilizer was helpful to improve the net photosynthetic rate of J. regia‘Wen185’