Abstract: The formation mechanism of geothermal anomaly in Sanhejian mine field is studied from both aspects:heat source and teat-forming environment,it is considered that the following factors are the main causes resulting the geothermal anomaly in mine field:the base of coal measures in mine field is located in relatively raised tectonic setting,resulting the increase of geothermal flux;the strata with different thermal conductivity are superimposed,and the heat concentrated in coal measures is not easy to escape,resulting the increase of geotemperature,the movement of groundwater is weak,it has a little influence of the drop in temperature,etc.