Heavy metal mercury (Hg) is one of the most seriously polluted heavy metals in the soil of Liaocheng, China. But the source of Hg is still not clear. In this study, 85 soil samples were collected in the entire area of Liaocheng to obtain the spatial distribution of Hg. The geological accumulation index was used to evaluate the pollution in the study area. The results showed that the average value of Hg exceeded the background value of Shandong Province, and in most areas of Liaocheng, Hg was in a light–medium pollution. In addition, the paper found obvious spatial heterogeneity of Hg. So, the study area was divided into 2 parts according to the results of geological accumulation index - I_geo: the lowvalue areas and high-value areas. They were also the two layers of dependent variable in the analysis of GeoDetector. It was used to find the source of heavy metal Hg pollution based on seven influencing factors: soil pH, soil organic matter, land use type, soil subcategory, GDP, distance from roads, and distance to water. Based on the results of the GeoDetector, the main factors affecting Hg in the I_geo lowvalue area were organic matter and soil type. Thus, the source of Hg in this area was mainly natural factors such as soil parent material. While in the I_geo high-value area, the paper found high-density and high-polluting industries with the Point of Interest data of factories and enterprises. It indicated that waste water, waste gas, waste residue generated in the production process of these industries were the main source of Hg pollution.