Using a portable photosynthesis system, we measured the leaf gas exchange characteristics of Artemisia ordosica, a dominant shrub species in semiarid areas of Northwest China, from May to October 2012 to quantify the temporal variations and environmental controls of its photosynthetic characteristics. Results showed that the diurnal variations of net photosynthesis rate (P_n), transpiration rate (E) and water use efficiency (WUE) were all asymmetric around 12:00, being higher in the morning than in the afternoon. Daily mean P_n varied over the growing season, being highest in June \[(8.97±1.73) μmol CO₂·m^-2·s^-1\] and lowest in October \[(2.58±1.32) μmol CO₂·m^-2·s^-1\]. The apparent quantum yield (α) and the carboxylation efficiency (φ) of A. ordosica varied in the range 0.022-0.048 mol·mol^-1 and 0.125-0.268 mol·m^-2·s^-1, respectively. The maximum net photosynthetic rate at the optimum light intensity (P_nmax) and saturation intercellular CO₂ concentration (A_nmax) occurred on 13 September (24.89 μmol CO₂·m^-2·s^-1) and 31 July (77.23 μmol CO₂·m^-2·s^-1), respectively. The P_nmax was significantly correlated with the atmospheric relative humidity, and A_nmax was significantly correlated with vapor pressure deficit and soil volumetric water content at 30 cm depth. Our results indicated that the carbon assimilation of A. ordosica was primarily limited by moisture related factors, and the photosynthetic characteristics of A. ordosica reflected its adaptation to semiarid conditions with low water availability and high summer temperature. In addition, our study provides important eco-physiological parameters that may help develop processbased ecosystem carboncycle models.