Abstract: This paper focuses on comparison between Leymus chinensis and Stipa grandis in relation of photosynthetic rate and light intensity from the early stage of vegetative growth to the late growing period. The result of his study indicated that:#br#1. The increase of light compensation point was bigger in S. grandis than that in L. chinensis with the rising of light intensity.#br#2. High light intensity of saturation point occured at the peak period of vegetative growth and the fluctuation of it was higher in S. grandis thanin L. chinensis.#br#The values of high net photosynthetic rate and light intensity coeffic-ient were bigger in L. chinensis than in S. grandis and both of their highest values occured at the highest growth stage.#br#4. The relative photosynthetic rate was higher in L. chinensis than in S. grandis under 10 Klux light intensity.#br#5. They appeared very obvious corelations between the changes of photosynthetic rate and saturation light intensities of L. chinensis and S.grandis and the variation of their leaf water content.