Acacia mangium is one of the frequently-used pioneer tree species of re-vegetation in degraded hilly lands in the southern China. Transpiration of four sample trees estimated from the xylem sap flow was measured using the Granier’s heat-dissipation probes over a period of four months. Sapwood depth was highly correlated with the tree diameter at the breast height. Environmental factors including solar radiation, net radiation, air temperature, air relative humidity, soil moisture and wind speed were measured simultaneously with the sap flow. Time lag between the sap flow and canopy transpiration during the measurement period was found to be 1 h. Canopy stomatal conductance (g_s) of the Acacia mangium was calculated by inverting the Penman-Monteith equation. As the transpiration from Acacia mangium was strongly controlled by g_s, We have analysed the relationships between g_s and environmental parameters. The results indicated that g_s decreased exponentially with the increasing of vapour pressure deficit (VPD),with the additional effect from temperature and solar radiation. As the measurement was mainly undertaken during the wet season, no obvious water stress was observed. A Jarvis-type model was further set up to describe the response of the g_s with the environmental parameters. It performed well to express the variation observed in g_s. The sequence affecting the accuracy of model for environment factors is vapour pressure deficit > solar radiation > air temperature. This model will be very helpful to simulate the dynamic photosynthesis and as well to simulate the energy and water balances in the Soil-Plant-Atmosphere Continuum (SPAC). Our research also demonstrates that the Granier′s probes can offer a way to measure g_s accurately and continuously.