Based on tissue heat balance theory

thermal dissipation sap flow velocity probes (TDPs) were used to measure sap flow velocity of Pinus tabulaeformis at Xiaowutai natural reserve in northern mountain areas of Hebei province. To explore the response of stem sap flow to environmental factors

the air temperature

relative humidity

solar net radiation

total radiation

and wind speed were simultaneously observed from March

2015 to March

2016. The results showed: (1) Stem sap flow of Pinus tabulaeformis started in late April and ended in late October

which lasted for 184 days at the Xiaowutai areas. On sunny days

the daily change of stem sap flow velocity presented unimodal curve in different months. There were differences in starting

peak and ending time and changing rate of stem sap flow in different months. (2) The diurnal average of stem sap flow velocity reached more than 0.02 kg/(h·cm) in every month except for April and October

especially higher in May and August in which it reached 0.028 and 0.027 kg/(h·cm). The monthly peak change of stem sap flow velocity was the same as diurnal average change. (3) Stem sap flow velocity was positively correlated with air temperature

solar net radiation

total radiation

vapor pressure and wind speed

whereas a negative correlation with relative humidity was observed. Influence of environmental factors to stem sap flow velocity was in the order of temperature > solar net radiation > total radiation > relative humidity > wind speed. (4) Water consumption of individual tree was （2 679.58±579.83）kg in the whole growth season

and the largest water consumption was in May and August with （585.14±110.92）kg and（510.08±87.96）kg.