Abstract: Under dry-hot condition, water contents, free water contents, bound water contents, and the ratio of bound water contents/free water contents in the needles of Pinus caribaea were 55%~58%, 4%~7%, 50%~51%, and 8~12 respectively, indicating that bound water was major water status.Transpiration was regulated by temperature and the free water was the main water consumption of transpiration during the diurnal variations of transpiration rates.The water retention capacity of Pinus caribaea was stronger than that of P.yunnanensis.Under induced water stress by Polyethylene glycol, the chlorophyll contents were stable or increased a little.The amount of free proline accumulation increased greatly with the decrease of relative water contents, the perxoidase activity and superoxide dismatase activity were also obviously increased.These physiological characteristics were helpful for living and growing of Pinus caribaea under dry environment.