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.