Abstract: The characteristics and mechanism of 9 Platycladus orientalis provenances were studied With respect to their hydro-eeophysiologieal specifics，water parameters，photosynthesis，transpiration and water utilization efficiency based upon the quantitative model of comprehensive appraisal of drought tolerance for tree species．The results show that under normal water condition the cell elastic modulus of southern provenances (Queshan，Mianyang，Liping) are higher than that of other provenances，thus can maintain larger turgor pressure to facilitate better growth．Both their photo-synthetic rates and water consumption through transpiration are higher and their water utilization ef-ficiency are low．While under water stress condition their leaf water potential，cell elasticity，drought tolerance productivity and water utilization efficiency are worsened greatly revealing their weak adaptability to water stress．Only the cell elasticity of middle-north provenance (Fu county) has been increased under water stress．and the declining degree of its leaf water potential，drought tolerance productivity and water utilization efficiency is minimal，therefore it has the greatest ability to tolerate drought than other provenances．The response indications of leaf water potential．cell e-lastieity，drought tolerance productivity and water utilization efficiency for Northeast (Changzhi，Zanhunag and Yidu) and Middle (Chunhua and Changzhi) provenances reveal their medium ability of drought tolerance．

Key words: Platycladus orientalis, Provenance, Drought tolerance, Water potential, Net photosynthetic rate, Transpiration rate, Water utilization efficiency