By using thermal dissipation probe,sap flow of Pinus elliottii was measured with the circumstance factors recorded by radiation,temperature and humidity sensors.There was a high correlation between sapwood area of P.elliottii and diameter at breast height by quadratic function.Regressional analysis on the sap flow of P.elliottii in different growing periods and sapwood area showed that daily cumulative sap flow correlated linearly with sapwood area with all correlation factors higher than 0.95.Significant correlations also existed between daily cumulative sap flow per sapwood(qs)and three separate ambient environmental factors including canopy temperature(CT),canopy relative humidity(CRH) and photosynthetically active radiation(PAR).Multiple linear models of qs and environmental factors were developed at significant level,of which the sequence of correlated degrees was as follows: CRH>PAR>CT.