Abstract:A study on the photosynthetic physiological characters of the vegetative tillers and reproductive tillers of Axonopus compressus reveal that the net photosynthetic rate (Pn) and the water use efficiency (WUE) of the former are higher than those of the latter, while the respiration rate and the light compensation point (LCP)of the reproductive tillers are higher than those of vegetative tillers. Moreover, the reproductive tillers’ basal leaves are weak in photosynthetic capacity and their respiratory intensity is intermediate-stronger than that of the vegetative tillers but weaker than the respiratory intensity of the flag leaves of the reproductive tillers. As the apparent quantum yield (AQY) of modules of the two tillers of Axonopus compressus are higher than those of plants in general, the lawn grass thrives in the dim light and adapts itself to a shady habitat. The vapor pressure deficit (VID) of leaves is mended through the stomatal conductance(Gs) to modulate the loss of water by the feedback of transpiration(Tr).in the intense light, the stomatal conductance of modules of the two tillers descend gradually, but their transpiration rate and vapor pressure deficit continue to increase linearly. The fact shows that Axonopus compressus lacks a water-retaining machanism and is more adaptable to a water-saturated habitat.