Abstract: Forest evapotranspiration is an important component not only in water balance,but also in energy balance. It is a great demand for the development of forest hydrology and forest meteorology to simulate the forest evapotranspiration accurately,which is also a theoretical basis for the management and utilization of water resources and forest ecosystem. Taking the broadleaved Korean pine forest on Changbai Mountain as an example,this paper constructed a mechanism model for estimating forest evapotranspiration,based on the aerodynamic principle and energy balance equation. Using the data measured by the Routine Meteorological Measurement System and Open Path Eddy Covariance Measurement System mounted on the tower in the broadleaved Korean pine forest,the parameters displacement height d ,stability functions for momentum φ_m ,and stability functions for heat φ_h were ascertained. The displacement height of the study site was equal to 17.8 m,near to the mean canopy height,and the functions of φ_m and φ_h changing with gradient Richarson number R_i were constructed.