Soil organic carbon (SOC) is an important component of the global carbon cycle. Uncertainties remain about the estimation of SOC storage because of a lack of information about temporal SOC accumulation in deep soil layers. Four ages of a Black locust (Robinia pseudoacacia) revegetation chronosequence including 9 (ch9), 15 (ch15), 24 (ch24) and 34 years (ch34) in the hilly Loess Plateau region was selected for this study. Vegetation characteristics and SOC dynamics down to a depth of 2m were investigated along the revegetation chronosequence to determine the accumulation of SOC in the deep soil layer and its response to revegetation. The results showed that the deep soil layer of the hilly Loess Plateau conserved a large amount of soil organic carbon. Deep layer (50-200cm) SOC content (1.35-2.39 g?kg-1) was equivalent to approximately 25% of that found in the shallow layer (0-50cm). Deep layer SOC storage (26.28-46.50 t?hm-2) accounted for more than 50% of total SOC storage (0-200cm), and deep layer SOC storage was significantly higher than that found in the shallow layer. The results demonstrated that total SOC storage will be underestimated by approximately 1/3 in this region if SOC was only measured to a depth of 1m. When compared to ch9，SOC storage and SOC content in deep soil layer increased significantly after more than 20 years revegetation. Average SOC content for 10cm increments down to a depth of 2m for ch9, ch15, ch24 and ch34 were (1.65±0.05） g?kg-1, (1.70±0.06) g?kg-1, (3.10±0.12) g? kg-1, and (3.35±0.16) g?kg-1 respectively. As a vigorous accumulation exhibited in the mature phase (15-24a) of Black Locust, average SOC content of 2m was doubled after 20 years revegetation (ch24, ch34) compared to that of 9ch. And for the entire revegetation chronosequence (9-34a) the increase in SOC storage down to a depth of 2m (43.02 t?hm-2) was distinctly higher than that in 1m (34.65 t?hm-2). Unlike the shallow soil layer had significant differences in SOC content in adjacent increments (0-30cm), in the deep soil layer the differences were only 0.12-0.42 g?kg-1. Black Locust growing conditions (coverage, basal diameter and height) showed significant correlation with both deep and shallow SOC content, demonstrating the significant influence of deep-rooting vegetation to deep layer SOC and the integrity of the whole soil organic carbon pool. Our results indicated that SOC storage in the deep soil layer should be considered when estimating the effects of soil carbon sequestration of revegetation in the hilly Loess Plateau region.