The efficient mechanism of plant absorption, transmission and conversion of light energy are the core of photosynthesis. To clarify the photosynthetic adaptability and habitat suitability of four desert plants in Western Ordos, the LI-6800 photosynthesis system was used to measure diurnal variations in photosynthesis in four desert plants, namely, Tetraena mongolica Maxim, Zygophyllum xanthoxylum, Nitraria tangutorum, and Ammopiptanthus mongolicus in Western Ordos. The results showed that: (1) Significant differences existed in the net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), and intercellular CO₂ concentration among the four desert plants. (2) Pn of the four plants showed a "bimodal" curve. The order of Pn among the four plants was as follows: T. mongolica (4.37 μmol m^-2 s^-1) > Z. xanthoxylum (3.58 μmol m^-2 s^-1) > A. mongolicus (2.63 μmol m^-2 s^-1) > N. tangutorum (2.26 μmol m^-2 s^-1); this indicated that T. mongolica and its relatives have stronger photosynthetic physiological adaptability than the other plants. (3) According to the physiological and ecological factors that affect photosynthesis, Pn has an obvious positive correlation with Gs, Tr, and water use efficiency, but not with relative humidity. (4) The moisture is an important limiting factor for the growth of the four desert plants. The aimed to provide a basis for the protection of desert plants in northwestern China.