Abstract: The photosynthetic characteristic and its relation to ecophysiological factors in a eightyearold chestnut (Castanea mollissim) in high density (2m×3m） orchards were studied. The main results were as follows: 1. The net photosynthetic rate (Pn) was generally 4～10 mg. CO2. dm－2·h－1，which was obviously lower than the other fruit trees such as apple, pear etc.; 2. The changes of Pn in a day time showed a singepeak curve during the early and later growth stages, but it was a doublepeak curve during rapid growth stages (6～8 months); 3. The seasonal changes in Pn also showed a doublepeak curve, the two peaks occurred during the flowering stage and fruit fast growth stage, respectively. The seasonal changes in Pn showed to be closely related to the seasonal variations of chlorophyll, water and mineral elements (N,P,K)contents in leaves, but were not well related to the transpiration rate; 4. The Pn was affected by temperature and relative humidity of ari as well as directly constrained by intensity of photosynthetically active radiation(PAR).