Abstract: In order to solve the detection problem of high salinity roof water, a ground tunnel combined transient electromagnetic method (TEM) is proposed, which is received in the ground and emission in coal mine tunnel. Taking the mine with high salinity groundwater in Ningxia as research object, the reflection characteristics of the secondary field to the roof water are summed up by the theoretical numerical simulation. The theoretical feasibility of the combined transient electromagnetic method is proved. Based on the theoretical results, the field measured data are processed and analyzed, and the distribution of roof water is inferred. The exposure of the tunnel is in accordance with the measured result. Results show that the position and range of the relative working surface of roof water can be accurately reflected by ground tunnel combined TEM. The method is not affected by the low resistance shielding. It is suitable for the detection of high salinity roof water.