Abstract: This study deals with the changes of osmosis-regulating substances（proline, soluble sugar and soluble protein）of three common tree species in south China area, i.e., Evodia meliaefolia, Rhaphiolepis indica, and Zenia insignis, under drought stress by means of pot experiment, with an aim to prove the approach and mechanism of how the trial species adapt to the drought stress so as to provide evidence for species selection in south China limestone area. Major findings were as follows: in condition of drought stress, contents of proline and soluble sugar of all three species showed an increasing trend, which peaked under heavy drought stress. Among them, R. indica was the highest (proline 490.86 μg/g, soluble sugar 38.13 mg/g), while E. meliaefolia was the lowest (proline 278.33 μg/g, soluble sugar 27.74 mg/g), Z. insignis was moderate. The content of soluble protein approximated a parabola: first an increase, later a decrease. E. meliaefolia(5.97 mg/g) and Z. insignis(6.84 mg/g) peaked under light drought stress, while R. indica (7.44 mg/g) peaked in moderate drought stress. In condition of heavy drought stress, only R. indica’s content of soluble protein(53.64%) was higher than that of normal condition, which approximated a great osmotic adjustment ability. In conclusion, R. indica shows a great osmotic adjustment ability, which can well adapt to drought stress condition; Z. insignis takes the second place, and E. meliaefolia is the worst.