Abstract: Heading detecting of geological structures is one of the prominent problems in coalmine geology. According to the theoretic analysis, this paper describes that this problem can be solved by using Fixed Electric-Source Gradient （FESG） method. The model experiment has proved the geophysical foundation of this method that will be used in underground is existing, apparent resistivity can be used to distinguish between water-bearing structrures and not ones. The practical application results show FESG method is easy to arange eletrodes, and its data is clear, too. The resolution and interference refusing capacity of the FESG method are higher than others. And the application results of this method are obvious it is a good geophysical prospecting method used in underground and it has higher practical value,vast spreading vista.