Abstract:China’s permafrost area accounts for more than half of the national land area， and large areas of permafrost and thundersforms coexist，directly affecting the power system grounding performance. First of all，the conductive mechanism of frozen and thawed soil is analyzed，and a conductive model of frozen and thawed soil is constructed；then，a test platform of resistivity and electric breakdown characteristics of frozen and thawed soil is designed and built，and tests on four typical soils and fine sands in China’s permafrost area are conducted，the soil resistivity and critical breakdown field strength with the change of hydrothermal conditions is measured，and the essential reasons for the changes is analyzed. The experimental study shows that the influence of hydrothermal conditions on the resistivity and critical breakdown field strength of frozen and thawed soil can be divided into three stages：pure frozen soil section， frozen and thawed soil section and pure thawed soil section；the resistivity ρ and the critical breakdown field strength E_c are both decreased with the increase of temperature，but only in the frozen and thawed soil section，a jump occurs.