【Objective】The black soil region of Northeast China is an important commodity grain production base in China. However, long-term high-intensity reclamation and unprotected utilization have led to serious soil erosion and continuous reduction of black soil thickness. In some areas, the low-nutrient loess parent material was exposed, resulting in decreased land productivity, and food production was seriously threatened. However, determination of the distribution of soil thickness on the slope is challenging. The traditional soil thickness measurement methods, including the soil profile method, soil probes, and the drilling method, are inefficient and cannot ensure continuity along the slope. Therefore, this study aims to apply a new method, ground penetrating radar (GPR), to measure the continuous variation of black soil thickness on slopes. 【Method】In this study, the GPR was used to continuously measure the black soil thickness on three slopes (straight, convex, and concave) in northeast China. Firstly, two types of soil, black soil and loess parent material were probed in a wood box to investigate the effect of soil moisture and bulk density on the soil permittivity and to prove the feasibility of GPR determination for black soil thickness. Then, the accuracy of the GPR in measuring black soil thickness was verified in conjunction with field trial excavation profiles and pre-buried iron pipes. 【Result】(1) The soil permittivity increased and decreased with the increasing bulk density and soil moisture, respectively. The relationships among soil moisture, bulk density, and soil permittivity for both black soil and loess parent material can be represented by logarithmic equations with an accuracy of 95.26%~99.66%. (2) Compared with the actual thickness of the soil profile, the accuracy of GPR measurements for black soil thickness was 87.05%~95.58%. (3) The spatial distribution of black soil thickness differed among the three slopes. However, the overall wave-like variation was observed. Deposition occurred at the slope foot and the black soil thickness was thick, while the black soil thickness at the shoulder and back of the slope was thin where soil erosion was more serious. 【Conclusion】Soil moisture content and bulk density had a significant effect on soil permittivity and the soil permittivity decreased with the increasing clay content. Also, there were differences in the permittivity of black soil and loess parent material. It was observed that electromagnetic waves could be reflected at their interfaces, which means that GPR can be applied to detect the black soil thickness on loess parent material. Our analysis revealed that topographic factors significantly affected the spatial variation of black soil thickness among the three slope types studied. Based on these results, this study could provide an efficient and accurate method to investigate soil thickness for further evaluation and conservation of black soil resources.