Walnut (Juglans regia L.) is an important economic tree species in rocky mountain of North China, which plays a key role in adjusting agricultural structure and promoting farmers' economic income. As a kind of hygrophilous tree species, irrigation is the main measure for the walnut water management in the region located in semi-arid zone with limited water resource. So it is necessary to accurately evaluate water consumption of walnut trees during the growing seasons to enhance water use efficiency. The main purpose of this paper is to observe and analyze the individual walnut water consumption and its response to meteorological factors during the growing seasons. Sap flow of walnut trees was measured by thermal dissipation probe (TDP) method and meteorological factors, reference crop evapotranspiration were acquired by automatic weather station and local astronomy data. The study measured, analyzed diurnal and monthly sap flow characteristics of individual trees of Juglans regia L. and the relationship with meteorological factors, reference crop evapotranspiration on daily and monthly time scales in 3 consecutive growing seasons from 2008 to 2010. The fitted equations between sap flow and meteorological factors, reference crop evapotranspiration were established with the observed data from the year of 2009 to 2010. Finally, the simulated values derived from the fitted equation were compared with those measured in 2008. The results followed that diurnal variation of sap flow velocity showed broad-peak curve, which was consistent with that of solar radiation on typical sunny days, and narrow-peak curve was found during rainy days, which was mainly regulated by precipitation and vapor pressure deficit. Sap flow of walnut trees showed obviously seasonal variation, the maximum value occurred in May and June. The total sap flow of walnut during the growing season (April to September) from 2008 to 2010 was 893.23 L, 854.88 L, and 841.77 L, respectively. Average daily sap flow was 4.96 L, 4.75 L, and 4.68 L, respectively. The interannual difference of sap flow was mainly caused by rainfall. Sap flow of walnut trees had good correlationship with meteorological factors, reference crop evapotranspiration on daily and monthly time scales. Moreover, the correlationship on monthly time scale was better than that on daily time scale. The simulated values of walnut sap flow by fitted equation were good agreement with measured values in 2008 on daily and monthly time scales. The fitted equation could be used to evaluate walnut sap flow with the data of meteorological factors and reference crop evapotranspiration in the absence of long time sap flow measurements. The fitted equation was reliable to estimate walnut water consumption, and could be applied to guide the walnut tree water management in the local area.