Abstract: A comparing analysis on photosynthetic physioecological properties of Mosla chinensis under four moisture treatments with relative soil water contents of 100%,60%,40% and 20%, respectively, has proved that the diurnal mean values of net photosynthetic rate (P_Nmean),stomatic conductance (Gs) and water use efficiency(WUE) of plants are the highest under 60% soil moisture, the content of hlorophyll and the ratio of chlorophyll a to b are higher both under 100% and 60% treatments. Plants living in these moisture conditions have a stronger capacity to reduce the hurts caused by effulgence. The field study shows that the plants living in mesophytic to slightly humid environments grow well, but their colonizing ability in the environments is weak. These results indicate that the most suitable moisture niche for Mosla chinensis is mesophytic and slightly humid, and the fact that plants can not occupy the most suitable water habitat in fields may be one of the major reasons restricting the population to extent quickly.