Water amount stored in sapwood and its participation in sap flow cycle are considered to be one of the important mechanisms for trees' drought resistance. Based on monitoring the sap flux of Populus bolleana at crown base and stem base with thermal dissipation probe technique (TDP), combined with synchronous meteorological observation, this paper analyzed the relationship between sap flow fluxes and atmospheric evaporation potential(ET₀) at two positions. Results showed that sap flow flux at crown base (Q_u) was a reliable indicator for estimating sap flux of P. bolleana individuals. The average daily Q_u in typical sunny days from June to September was (7.61±0.65) L/d, which was higher than those in cloudy and overcast days by 0.41 and 2.71 L/d respectively. The sap flow flux in stem base (Q_d), varied greatly in different seasons, was lower than Q_u during the sunny days from June to August but reversed rapidly in late August following continuous rainfall, by which P. bolleana maintained water-balance and solved water deficit partly. After continued rainfall in late August, soil moisture improved effectively, so the percentage of nocturnal sap flux to total daily Q_d reduced from 31.98-35.36% to 6.72%-7.99%, by which water deficit could be compensated effectively. P. bolleana have experienced water supplement (in June), loss (in July and August) and re-supplement (in September) processes during the whole growing season. ET₀ was a reliable integrated variable for evaluating sap flow environment-driving effects which could be modeled well with Q_u by Logistic equation, the modeled results showed that the maximum of Q_u was 7.82 L/d. When ET₀ is more than 5 mm/d, Q_u and Q_d no longer increased, which is a kind of positive drought resisting strategy of Populus bolleana. The continuous rainfall in late August caused the ratio of transpiration to ET₀ (T/ ET₀) increased from 0.32 to 0.47, obviously, the improvement of soil moisture affected sap flux of P. bolleana significantly.