Abstract: Canopy stomatal conductance (g_s) is an important biological parameter to measure water vapor flux in canopy-atmosphere interface. Exploring characteristics of canopy stomatal conductance and its responses to environmental factors can offer theoretical evidence for conducting mechanism-based study of vapor exchange process in forest canopy. SF-L thermal dissipation probe was adopted to measure sap flow density (J_s) of Platycladus orientalis in 2014. The environmental factors including photosynthetically active radiation (PAR), vapor pressure deficit (VPD) and air temperature (T) were simultaneously observed. The canopy stomatal conductance was calculated, and the responses of g_s to environmental factors were analyzed. The results showed that the daily variation of sap flow density was of two-peak pattern curve, and the J_s in growing season was higher than in non-growing season. And the bigger DBH was, the higher J_s would be. The daily variation of canopy stomatal conductance was similar to the canopy transpiration of per leaf area (E_L), which was of two-peak pattern curve. The g_s and E_L in growing season were higher than those in non-growing season. The canopy stomatal conductance and air temperature presented parabolic relation, and g_s reached peak valley at around 10 ℃. Taking the value of 400 μmol·m^-2·s^-1 as the PAR thre-shold, when PAR was under this threshold, g_s was positively correlated with PAR. When PAR was beyond this threshold, the correlation between g_s and PAR would be small. The relationship between canopy stomatal conductance and vapor pressure deficit was negative logarithmic function. As VPD increasing, g_s decreased gradually. Higher air temperature and photosynthetically active radiation, and lower vapor pressure deficit contributed to higher canopy stomatal conductance of P. orientalis and could promote greater canopy transpiration.