Abstract：Considering the shortages of late time apparent resistivity interpretation of vertical component in Transient Electromagnetic Method (TEM) advanced prediction at present，this paper discusses full space and full zone apparent resistivity method of arbitrary coplane vertical magnetic component in tunnels. First，calculate the full space vertical response of loop source from response in homogeneous full space of electrical dipole and vector addition. Then，deduce the full zone apparent resistivity definition of TEM coplane vertical magnetic field from full space time domain response. Lastly，analyze the influence of tunnel cavity and aquifer structure. By comparing the method in this paper with traditional method，the results show that our method can effectively avoid the influence of tunnel cavity and is better in aquifer structure detection.