<p>Magnetic susceptibility (MS) is a magnetic parameter that reflects the intensity and nature of a material’s response to an external magnetic field. It can sensitively indicate magnetic particles associated with anthropogenic activities and serves as an important proxy for soil heavy metal pollution. This study focused on the topsoil of Yinchuan City, a representative urban area in northwestern China. A total of 366 surface soil samples were collected via grid and profile-layering methods. MS was measured to analyze spatial distribution, vertical variation patterns, and correlations with heavy metal concentrations. By integrating MS data from cities of different administrative levels across Northwest China, the applicability of the Dual-Threshold Magnetic Susceptibility Evaluation Map (DTMS Map) was validated, and the regional soil pollution status was assessed. The results showed: (1) the mass-specific low-frequency magnetic susceptibility (χ_lf) of topsoil in Yinchuan was generally low but exhibited higher values in traffic, industrial, and commercial zones; (2) the χ_lf was significantly correlated with Cd, Cu, Pb, and Zn, with Cd identified as the dominant pollutant (70% above background values). Cr and Ni mainly originated from natural sources, while Cd, Cu, Pb, and Zn were primarily attributed to traffic and agricultural inputs. The overall ecological risk was low. (3) Across Northwest China, 26.8% of topsoil exhibited contamination characteristics, with MS increasing from northwest to southeast. This confirms that MS as an effective tool for rapid heavy metal assessment, and demonstrates the suitability of the DTMS Map for identifying urban soil pollution in northwestern China.</p>