Abstract: Selecting the dominant tree species Quercus fabric in three root underground habitat types (the dolomites of low oblique occurrence with multilayer space, middle oblique occurrence with multilayer space, and high oblique occurrence with multilayer space) in Karst area as test object, this paper studied the foliar δ¹³C value and its correlations with habitat soil conditions, and the plant water use efficiency. There existed remarkable differences in the foliar δ¹³C value of Q. fabric among the three habitat types, being decreased in the order of low oblique occurrence with multilayer space type (-26.35‰) > high oblique occurrence with multilayer space type (-26.66‰) > middle oblique occurrence with multilayer space type (-27.07‰). Accordingly, the plant water use efficiency decreased in the same order. The foliar δ¹³C value had significant correlation with habitat soil moisture content, but less correlation with habitat soil elements contents. The δ¹³C value increased with the decrease of soil moisture content and soil fertility.