Soils exhibit various development trends due to differences in initial conditions and external driving forces, leading to spatial and temporal variation in their properties. This study integrates digital soil mapping (DSM) with a modified evolutionary pathway approach (Δcomplexity) to quantify horizontal and vertical soil heterogeneity across an agro-pastoral transitional zone (APTZ) in northern China. We focused on particle size distribution (PSD) and magnetic susceptibility (MS), and quantified Δcomplexity between different soil depths to provide valuable insights into soil-landscape evolution. This study measured the PSD and MS of 1317 samples and determined Δcomplexity for 148 catchments in the study area. The R² for the prediction accuracy of DSM ranged between 0.481 and 0.729. The Δcomplexity of PSD spans from -0.089 to 0.042 % cm^-1 for both deep and shallow layers, whereas that of MS ranges from -0.6 to 0.96 10^-8 m³ kg^-1 cm^-1. Vertical heterogeneity, which is determined by the positive and negative shifts in Δcomplexity in every 5 cm soil, is primarily associated with soil forming factors such as parent material, topography and vegetation, and it is further regulated by tree throw and human activities. For horizontal heterogeneity, which derived from pedogenesis and also soil redistribution induced by both water and wind erosion, is determined by the positive and negative variations in both shallow and deep complexity. Our approach enables the identification of highly heterogeneous areas that may be particularly sensitive to soil change and degradation. It offers a transferable framework for assessing soil development and guiding sustainable land use. The soil Δcomplexity metric provides a promising tool for analyzing and visualizing the state and trends of soil-landscape evolution, and provides a scientific basis for informing land management decisions.