Photosynthesis and transpiration of Artemisia sacrorum were studied using the Li-6400 portable photosynthesis system in Loess Plateau region. The results showed that the diurnal variation of net photosynthetic rate （Pn） in A. sacrorum was single-peak curves from June to September. The diurnal variation of Pn was a bimodal curve and photosynthesis got into midday depression at 14:00 in May. The light compensation point （LCP） and the light saturation point （LSP） of A.sacrorum were 44.1 μmol·m -2 s -1 and 351 μmol·m -2 s -1 ,respectively. The LCP was higher than that of typical sun plants and the LSP verged on that of typical sun plants. This indicated that A.sacrorum was a sunny and typical sun plant. With PAR increasing, Tr was increasing along and had no saturation peak. When PAR was less than 160 μmol·m -2 s -1 , the water use efficiency （WUE） of A.sacrorum increased greatly. When PAR varied from 160 to 2 000 μmol·m -2 s -1 , WUE changed from 2.5 to 3.39 μmol CO2·mmol -1 H2O. It was proved again that A.sacrorum was a sunny plant.
