Use LI-6400 photosynthetic system ,LI-3000A Leaf area meter etc. to determine photosynthesis rate and transpiration rate of the dominant plants of T. serpyllum and H. rhamnoides communities. Meanwhile water content of the plants, soil moisture, above-ground biomass and root-top ratio were determined too. After calculation of the data, diurnal changes of photosynthesis and transpiration rate, water use efficiency of the dominant plants in the two communities were described. In addition physiological water characteristics were discussed according to water content, water saturation deficit and water potential of the dominant plants leave. Also, according to transpiration,water loss and soil moisture, it was proved that ecological water of the two communities appeared difference obviously. 