A thermal dissipation probe (TDP) was used to continuously measure the sap-flow rate of apple tree in Changwu county in loess tableland area of China from July to October, 2012. The effect of meteorological factors, soil moisture and other environment factors on sap flow was analyzed. The results showed that diurnal variation of the sap-flow rate of apple tree was a single peak curve in both sunny and rainy days. On sunny day, the sap-flow started more early and stopped more lately than on rainy day. The sap-flow rate of apple tree was positively correlated with solar radiation, vapor pressure deficit, atmospheric temperature and atmospheric relative humidity with a linear equation, and negatively correlated with air relative humidity. The dependency of sap-flow rate on various meteorological factors on the sunny day was more significant than on the rainy day. In addition, the sap-flow rate of apple tree varied distinctly in different environment conditions of soil moisture. Under the water stress condition, the sap-flow rate was significantly lower than that under the moist soil condition. The change of sap-flow rate showed a broad-peak curve, indicating that the transpiration was higher under the moist soil condition.