Abstract: To evaluate the ecological adaptation mechanism of Haloxylon ammodendron and H. persicum from Ningxia, the host of Cistanche deserticola, the chlorophyll fluorescence under dehydration and diurnal variation was determined by IMAGINGPAM method. The results showed that H. ammodendron had higher photosynthetic electron transport activity (F_v/F_m), photosynthetic efficiency (q_P), and PSⅡ electron transport activity (ETR) than H. persicum. After 48 h dehydration, the chlorophyll fluorescence and waterretaining property of H. ammodendron were significantly higher than those of H. persicum. The significant difference in diurnal variation between H. ammodendron and H. persicum was observed and a‘V’trend was exhibited. It suggested that H. ammodendron had a stronger ability to adapt to the environment and had wider distribution, while H. persicum was limited by water and light and had narrow distribution.