Abstract: Studies on the effect of nitrogen addition on the eco-physiological traits and growth of forests are of great importance, providing basic information for assessing the mechanism of forest dynamics. Here, we conducted a metaanalysis upon 32 studies to reveal the response of tree photosynthesis to N addition. We found that tree photosynthetic rate increased as a whole (10.24%), and the influence of N addition on temperate trees (11.45%) was higher than that on tropical trees (10.32%); broadleaved tree species was more sensitive to N addition than conifers. The responses ratio of tree photosynthetic rate varied with N addition level and experimental duration. When the nitrogen addition level was less than 25 kg·hm^-2·a^-1, tree photosynthetic rate increased (6.28%) insignificantly. The tree photosynthetic rate increased with the nitrogen addition level, with increments of 13.50% and 13.09% at 25-50 and 50-100 kg·hm^-2·a^-1, respectively. However, the tree photosynthetic rate increased insignificantly when the nitrogen level was more than 100 kg·hm^-2·a^-1. Generally, the photosynthetic rate was improved significantly in the experiment less than 5 years, but inhibited in the experiment longer than 5 years. The inhibition effect became insignificant in the experiment longer than 10 years. Excess nitrogen addition would lead to nutritional imbalance in plants (increased foliar N and decreased foliar P, K, Ca and Mg), which may contribute to the changes of photosynthetic pigments and enzyme activities.