The invention relates to a method for determining excavation soil resistivity, which calculates the equivalent resistivity of excavation soil by taking the proportions of the volume of soils with various resistivities in the excavation soil in the total excavation as weights and adopting a weighted average method. The method can reduce the calculation error of the excavation soil resistivity, thereby reducing the usage amount of metal materials when ground net grounding conductors are designed and greatly saving the ground net construction funds.