Abstract: The yearly variation water potential and the daily process of transpiration rate of chinese pine (Pinus tabulaeformis) plantations in Beijing, aged 8 years, coming from 13 provenances of 7 climatic ecotypes, were determined with presseue-chamber technique and BL8503 porometer. The result showed that for all provenances, the minima of water potential are found in winter (–19.35 bar) and in the period of high temperature and dry seasons (–14.81 bar). There are distinct differences among the values of water potential from different provenances, the largest for the provenances of northeastern ecotype and the least for southern ecotype. The value of water potehtial is obviously related to the mortality in winter, the populations originning in south have the lowest water potential and the highest mortality in winter. The daily and seasonal change of transpiration rate for all provenances are apperently regular. The daytime course looks like a convex curve with high value in midday and low value in early morning and night. The curve of yearly course has two peaks. Clear differences are observed among the transpiration rates of different provenances, the northeastern ecotype with the highest value and the southern ecotype with the lowest one.