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Water-deficit stress is an important limitation for agricultural production in semi-arid region. The aim of this study was to investigate the effects of water supply on the growth, water potentials of leaves, gas exchange, proline, and soluble sugars accumulation in the herbal plant Saposhnikovia divaricata. The herb was exposed to four water supply treatments, 450 mm, 400 mm, 300 mm and 200 mm of total water supply, distributed over the growth period in proportion, which modeled the seasonal mean precipitation the plants may experience in North-East China. The results indicated that the photosynthetic processes in S. divaricata depended strongly on the water supply conditions. Both stomatal and non-stomatal limitations were responsible for photosynthetic decline of S. divaricata in the midday. The water potentials of leaves (psi leaf) were gradually decreased in four treatments as drought stress increased. A strong increase of total leaf area, biomass and the net photosynthetic rate was observed as a result of 400 mm-treated plants, but severe water stress (200 mm treatment) significantly decreased the total leaf area, biomass, chlorophyll content and gas exchange (P<0.05). By accumulating proline and soluble sugars, S. divaricata could adapt to the water shortage condition. According to these results, rainfall containing 300 and 400 mm of precipitation during the growing season is readily available in arid and semiarid territories of North-East and North-West China, the expansion of the cultivation of S. divaricata is feasible and can be profitable there, thus alleviating the pressure on wild resources.