Abstract：As in other electromagnetic sounding methods,static offset and correction also arise in frequency-domain electromagnetic sounding. We analyse the generation mechanism of static offset under the boundary conditions of different substance-in-terfaces. The phenomenon is clearly explained that surface electric inhomogeneity makes frequency-sounding field components increase or decrease with a certain ra-tio,without dependence on frequency.Having analysed the frequency sounding data in Henghe coal mine in Shandong Province,we deem that low-pass filtering methods such as spacial filtering work on condition that the effect due to surface electric inhomogeneity can be considered as "high frequency"when it is compared to the electric effect of geologic structure (orbody). However, phase correction method has no such limitation, and it has good adaptability,but less stability in inversion sometimes.
