Abstract: Photosynthetic reactions by intensity of the sunlight, photosynthesis rate in a whole fine day and its affected factors were detected on leaves of Mei tree (Prunus mume) in early June, 1983 and 1984. The results showed that the light compensation point and light saturation point of Mei tree's leaves are 2-3klx and 30-40klx, respectively. Photosynthesis rate of the leaves reaches two peaks at 10 and 15 hour in a fine day during the growing season. Photosynthetic productivity of the leaves is affected by temperature and relative humidity of air as well as directly constrained by intensity of the sunlight.