Thermal dissipation method has important advantages over other techniques for measuring tree and bush transpiration, which can distinguish between plant and soil evaporation, and can be used to measure transpiration of different species in a mixed plant stand. Hence, the method has been widely applied by tree physiologists and forest hydrologists. An important potential limitation, however, is that the calibration of the Granier's experiential formula is based on an empirical relationship between temperature difference and sap flux density, rather than on the physical properties of heat transfer in sapwood. In order to study the accuracy of Granier's empirical formula in calculating transpiration water consumption of individual tree, eight Platycladus orientalis trees were selected as representative diffuse-porous to validate the accuracy of Granier's empirical formula in Xiaolangdi forest ecosystem research station of state forestry administration from May to June in 2011. The sap flux densities of P. orientalis under different pressure at water column heights of 15, 30, 50, 70 and 90 cm were measured by thermal dissipation method and compared with weighing method. The relationship between sap flux density of P. orientalis and temperature difference's coefficient (K) obtained using regression analysis method was established. The results showed that corrected Granier formula was F_d=0.0115K^0.5581 (R²=0.8319) based on individual P.orientalis. the calibrated Granier formula was obviously different from Granier's original formula (F_d=0.0119K^1.231 (R²=0.96)). The coefficient α(0.0115) of corrected Granier formula was similar to that of the Granier's original formula, but the coefficient β0.5581) of the corrected Granier formula was one order of magnitude smaller than that of Granier's empirical formula, and their quantitative difference was 54.66%. Compared with the sap flux density measured by weighing method under different pressure at water column heights of 15, 30, 50, 70 and 90 cm, the average values of the corrected Granier formula was (6.70±0.02)% higher, while the average values of original Granier formula was (78.53±0.04)% lower, indicating that estimations of sap flux density of individual P. orientalis by corrected Granier formula were of higher precision. Therefore, the corrected Granier formula would be apply to calculate sap flux density of P. orientalis. Nevertheless, an error-modified formula based on thermodynamics theory must be provided to ensure the accuracy of sap flux density derived from the original Granier empirical formula.