Abstract: The main photosynthesis indexes of Distylium chinense were measured with CB-1102 portable photosynthesis instrument under natural condition. The results showed that the daily progress of photosynthesis rate(Pn) was an obvious double-peak curve. The peak values were at 12:00 am and 16:00 pm respectively. Light noon break occurred at about 14:00 pm. The maximum net photosynthesis rate occurred at 12:00 am and was only 9.37 μmol /m²·s. The curve of diurnal variation of transpiration rate was one peak curve, but the peak value appeared at 12:00 am to 16:00 pm, which was 4.34 μmol/m²·s or so. Photosynthesis rate was also affected to different extents by eco-physiological factors such as transpiration, temperature, Ci and PAR.