Abstract:During the flowering period, the diurnal changes of Pn of Scutellaria baicalensis and environmental factors in three different habitats (Linjiang, Changchun, Taonan) were measured, and the obtained data were analyzed to explore the diurnal changes of Pn and its relationship with environmental factors from three different ecological zones. The conclusion will provide the theoretical basis of physiology and ecology of photosynthesis for scale field cultivation of S. baicalensis in Jilin province. The results indicated that the diurnal changes of Pn of S. baicalensis in three different habitats showed a typical double-peak curve with a slight “midday depression of photosynthesis”, and the Pn reduction at noon originated from the co-effects of stomata factor. There was a significant (p<0.01) positive relationship between the Pn and PAR in the three zones. The positive relationship was significant (p<0.01) between the Ca and the Pn in Changchun, and significant (p<0.05) between the relative humidity and the Pn in Taonan. The direct impact of environmental factors to Pn in three different habitats was the order of PAR>Ca>Ta>RH>TL in Linjiang, Ta>RH>PAR>Ca>TL in Changchun, PAR>RH>TL>Ca>Ta in Taonan. Low air humidity was an important ecological factor in determining the “midday depression of photosynthesis”. High temperature and humidity in Linjiang, low CO2 concentration in Changchun, and low relative humidity in Taonan were the main environmental factors influencing the net photosynthetic rate of S. baicalensis, in which was affected by the integration and interactions of PAR, Ta, RH, and Ca. The dominant factor for the net photosynthetic rate of S. baicalensis was different in different habitats.