The diurnal changes in net photosynthetic rate (Pn) of Saposhnikovia divaricata (Turcz.) Schischk. and their relationships with photosynthetic active radiation (PAR), atmospheric CO2 concentration (Ca), ambient temperature (Ta), leaf temperature (Tl) and relative humidity (RH) were studied systematically in different periods. This knowledge is essential for formulating generalization regarding the cultivation of the species in Jilin Province. Results showed that the diurnal changes in Pn of the species in different periods were similar and could be expressed as two-hump curves, reflecting a significant middy depression. The decrease in Pn during midday was mainly resulted from non-stomatal limitation in July, but stomatal limitation occurred in August and September. High temperature and low relative humidity were critical factors constraining Pn in July. The non-synchronous change of Pn and E were the main reason leading the variations of WUE. PAR affected Pn, synthesis and transformation of organic matter, which restricted the production for S. divaricata. There was a significantly and positively correlation between the Pn and PAR (P<0.05). The responses of S. divaricata leaves to the environmental factors were different during growing season, and the direct effects of environmental factors in three different months were of the order: Ta＞PAR＞Tl＞Ca＞RH in July, Tl＞PAR＞Ta＞RH＞Ca in August, Ta＞PAR＞Tl＞Ca＞RH in September.