Abstract: Dimethoate is a highly efficient, broad-spectrum organophosphorus pesticide. However, the environmental pollution derived from its extensive application in agricultural fields has emerged as a major global environmental concern. To clarify the residual risk and spatial distribution characteristics of dimethoate in farmland soils of the black soil region in Heilongjiang Province, we collected 114 surface soil samples during 2023–2024. Gas chromatography (GC) was employed to determine the residual concentrations of dimethoate, while geostatistical methods, human health risk assessment model, and ecological risk assessment model were integrated to systematically analyze its residual levels, spatial distribution patterns, and multi-pathway exposure risks. Our results showed that the residual concentrations of dimethoate in the study area ranged from 0.025 to 0.115 mg·kg⁻¹. Spatially, the residues exhibited a distribution pattern of higher concentrations in the southern and western regions compared to the northern and eastern parts. Health risk assessment revealed that the total non-carcinogenic hazard index (HI) value was 3.49×10⁻⁴ for adults and 2.98×10⁻³ for children, respectively, which is far below the safety threshold of HI<1, indicating that the current residual levels would not pose significant non-carcinogenic health risks to the local population. Furthermore, the ecological risk assessment based on chronic toxicity to earthworms demonstrated that the risk quotient (RQ) of dimethoate to earthworms ranged from 0.089 to 0.402, with most sampling sites classified as medium risk and no high-risk sites identified. These findings indicate that the current residual levels of dimethoate pose negligible risks to human health, but present potential chronic risks to the soil ecosystem. The results of this study provide direct scientific evidence for the hierarchical environmental risk management and targeted prevention and control of dimethoate in this region.