Magnetic micro-particles in soil polluted by heavy metals around 13 cities were collected for the purpose of determining their environmental significance. They can be used as tracers for the source of heavy metals in soil because the microstructure and mineral component characteristics show evidently their derivation from coal combustion. The magnetic susceptibility of falling dusts containing abundant magnetic micro-particles is much higher than the average value of urban soil, which explains clearly the reason why soil polluted by heavy metals always has high magnetic susceptibility. Finer particle sizes of magnetic micro-particles have higher magnetic susceptibilities, which facilitates the diffusion of heavy metal pollution for a long distance. The occurrence rates of the magnetic micro-particles in soil collected from 13 investigated cities all exceed 80%, which indicates the universal distribution of magnetic micro-particles in soil of urban and surrounding areas. The average content of the magnetic micro-particles in 5 kg soil sample collected from Beijing varies in the range of 30～7070 mg with the highest being 267 g. Magnetic micro-particles can be regarded as carriers of heavy metals in soil because all the eight heavy metals could be detected in chemical component analysis and the content is 2～25 times higher than the soil eco-geochemical reference value of China's eastern plain region. Results of correlation analysis show that in most cases there exists a significant correlation between content of heavy metals in magnetic micro-particles and that in soil polluted by coal combustion. The contribution rate of magnetic micro-particles to heavy metal accumulation in soil is generally lower than 1% though it could reach 10% or 60% in soil with much more magnetic micro-particles. It must be emphasized that the contribution rate mentioned above only shows the trend of the environmental effect of coal combustion because magnetic micro-particles do not constitute all the pollution components produced in the process of coal combustion and the content of magnetic particles can not be quantified due to the unavoidable loss in the process of elutriation. Nevertheless, the above phenomena could at least prove that magnetic micro-particles can be used as an easy means for connecting media that contact heavy metal pollution in soil of cities with atmosphere pollution produced by coal combustion. As heavy metals in magnetic micro-particles are commonly very inactive, the evaluation criterion range of heavy metal content in eco-geochemical assessment can be properly broadened according to the content of magnetic micro-particles in areas around coal combustion factories. At the same time, it should be taken into account that heavy metals in magnetic micro-particles can also be released in some extreme conditions such as low pH or high salt content. Forecast should be conducted so as to prevent the environmental disaster produced by activated heavy metals in magnetic micro-particles.