Pear jujube (Ziziphus jujuba Mill. grafted on wild jujube) is widely cultivated in the Loess Plateau region of China. However, pear jujube culture has been constrained by the wasteful use of limited water supplies that characterizes traditional irrigation, which has restricted the development of local agriculture. Thus, there is a need to develop new irrigation scheduling techniques that optimize water use. This paper aimed to determine a suitable soil water potential measure based on pear jujube tree responses to different soil water potentials during the fruit development period in the Loess Plateau. Fruit development is divided into two periods, i.e., the slow-growing fruit stage, where the main fruit process is cell differentiation, and the fast-growing fruit stage, when the cells expand. Four soil water potential levels were tested with four-year-old pear jujube trees. It was found that the maximum daily trunk diameter increased slowly during the slow-growing fruit stage while high soil water potential decreased the proportion of fruit abscission. The fruit abscission rate decreased significantly when the soil water potential was higher than -84 kPa. The maximum daily trunk diameter and relative leaf water content indicated the pear jujube water content during the fast-growing fruit stage. Thus, higher soil water potential resulted in a greater maximum daily trunk diameter and increased relative leaf water content. Furthermore, the percentage of fruit abscission was negative, i.e., fruit set number exceeded fruit abscission, when the soil water potential varied in the range of -41 kPa to -51 kPa during the fast-growing fruit stage. Fruit setting occurred in treatments where the soil water potential was higher than -84 kPa, whereas trees did not set fruit after receiving full irrigation that produced a soil water potential of -461 kPa in early experiments. However, fruit that set during the fast-growing fruit stage were always small because they had less time to grow. Thus, the single fruit weight with a full irrigation treatment was lower than other treatments. The soil water potential was similar to the control treatment after drought stress (-461 kPa), but leaf photosynthetic function and chlorophyll content were affected, i.e., the leaf photosynthetic function was decreased and the chlorophyll content was the lowest among all treatments. The low chlorophyll content decreased the leaf photosynthetic function. We found that mild controlling the soil water content could increase the single fruit weight with no effect on production. This study showed that a suitable soil water potential during the fruit development period was -41 kPa to -84 kPa, because this treatment increased the leaf water use efficiency and the single fruit weight, which compensated for the lower number of fruit.