Based on the differential equation of heat conduction

this article discusses the convection influence on earth′s temperature and the relationship between geothermal characteristics and depth.It gets the analytical expression of geothermal characteristics with depth

proposes the method and procedure for using the least square method to analyze geothermal data and gets the seeping characteristics of groundwater.An engineering problem example is given

which can be explained by this relationship to choose the position of Gaoligong tunnel going through.It analyzes the geothermal characteristics and gets seeping division.It considers that the warm groundwater appears in the north part to the Huangcaoba fault

can′t flow to the south part of it.This fault cuts off warm groundwater flow

makes the north and south parts become separate area.It gets the results that the aim position of the tunnel is low geothermal area.This conclusion can give us proof to avoid the geothermal hazard of tunnel reasonably.