The lack of water resources in the arid northwest of China has seriously restricted the growth and efficient production of fruit trees. Zaosu pear (Pyrus ssp. Va., Zaosu) is the main variety of pear cultivation in Gansu Province and one of the pillar industries for local economic development. This study compared the changes in sap flow of Zaosu pear trees in different tree shapes (Y-shaped, single-armed, and spindle-shaped trees) in different months, weather conditions, and developmental stages, as well as the relationship between sap flow and meteorological factors, to provide a theoretical basis for the selection of Zaosu pear tree shapes in arid areas. The results showed that the daily variation of sap flow was affected by tree shape and weather conditions. The start time of sap flow of the single-arm tree was later than that of the Y-shaped and spindle-shaped trees in spring, but the average daily sap flow in the growth and development period (June, July, and August) on sunny days was 73.05, 51.41, and 76.33 g h-1, respectively, and the daily cumulative sap flow could reach 3503.4, 2467.4, and 3664 g h-1, which were significantly higher than those of the Y-shaped and spindle-shaped trees. Different growth stages had a significant effect on sap flow, and the peak sap flow was the highest during the fruit expansion and maturity stages. This stage was the critical period for water demand. The sap flow of the three tree shapes started at 8:00 AM, reached a peak at 1:00 PM, and stopped at 7:00 PM in the first fruit expansion, the second fruit expansion, and the maturity stage. The sap flow of the single-arm tree was the largest. Correlation analysis showed that sap flow was significantly positively correlated with temperature and solar radiation. The higher the temperature, the stronger the transpiration, the greater the sap flow, and it was significantly negatively correlated with humidity. In summary, the single-arm tree shape is more suitable for cultivation in arid areas and has good water use efficiency and environmental adaptability.