Black locust (Robinia pseudoacacia) are widespread across the Loess Plateau of China. It's of great importance for understanding the variation of soil water in black locust plantations under restoration to study dynamic of soil water in black locust plantations with different restoration years and it's temporal stability by the substitution of space for time with restoration time going. Based on long-term in-situ observation of soil moisture in growing season from May 2014 to October 2018, relative difference and Spearman rank correlation analysis were used to study the temporal stability of soil water in 15 a, 20 a, 30 a and 35 a black locust plantations. Results showed that (1) the soil water storage of black locust plantations with different restoration years was significantly different, the soil water storage increased first and then decreased, with the increase of restoration years, and the order was 30 a (184.9 mm) > 20 a (184.6 mm) > 35 a (150.8 mm) > 15 a (128.8 mm). As soil depth deepened, soil water decreased with the increase of soil depths, but does not change regularly with restoration years; results indicates that soil moisture is mainly affected by precipitation and vegetation growth, and its spatiotemporal distribution patterns of variability (CV, Coefficient of Variation) also indicates that stability of soil moisture increased with soil depth increasing accordingly; (2) Temporal stability of soil moisture was established by relative difference analysis and index of temporal stability at black locust plantations with different restoration years, the representative depths of 15 a, 20 a, 30 a and 35 a were 80 cm, 100 cm, 80 cm and 150 cm soil depth, respectively, which were all close to 100 cm soil depth; (3) Spearman rank correlation analysis shows that the upper and lower soil layers have their own time stability pattern; (4) The results of linear regression and Nash-coefficient show that it is acceptable to obtain the representative depth of soil water by relative difference and index of temporal stability, but there are some uncertainties remained, which should be taken into account in the further region soil water simulation study. (5) Results of Grey relational analysis shows that soil texture (Sandy), soil total nitrogen (STN), soil bulk density (BD), soil organic carbon (SOC), soil total porosity (STP) and slope degree are the major influencing factors on time stability of soil moisture at different restoration years which indicates that the spatiotemporal dynamics of soil moisture are influenced by heterogeneity of environmental factors. The results may provide theoretical reference and scientific basis for further ecological civilization construction in the Yellow River Basin.