Purpose: This study aims to clarify the spatial variability and characteristics of the distribution of soil properties and erodibility on a typical river alluvial and marine sedimentary plain in eastern China.Methods: We collected soil samples and measured the soil properties for 2955 sampling points in the study area. The spatial variation and distribution of the variables were analyzed using Moran’s I, semivariogram, and sequential Gaussian simulation (SGS) methods, and a spatial risk analysis of soil erodibility (K factor) was performed based on 500 realizations of SGS.Results: The mean K factor, pH and sand, silt, clay, and organic matter contents were 0.0302 t·ha·h·ha−1·MJ−1·mm−1, 7.07 and 50.36, 30.05, 19.58%, and 27.62 g kg−1, respectively, all indicating moderate spatial variability. All variables were strongly globally autocorrelated (Moran’s I > 0.3). The ratios of spatial structure indicated that all variables had moderate or moderately strong spatial dependence. The spatial distributions of the variables were strongly influenced by geography, with higher sand contents and pHs along the abandoned Yellow River, the eastern coastal area, and the alluvial area of the Yangtze River Delta. Silt, clay, and organic matter contents, however, had opposite spatial patterns. Areas at a high risk of soil erodibility were along the abandoned Yellow River, the eastern coast, and the southwest. The areas with probability of soil erodibility risk > 60, 80, and 90% accounted for 51.94, 33.45, and 24.34% of the study area, respectively.Conclusions: This study provides a methodological reference for research into spatial mapping and an empirical basis for agricultural management and erosion control that can be applied to other river alluvial and marine sedimentary plains.