Electromagnetic waves in SLF (super low frequency) frequency band can be transmitted by powered generator using geophysical theory combined with radio-physical theory. The artificial signals can be measured in a quite large area on earth surface for investigation of the space electromagnetic field and crust conductivity structure. The method is a useful tool to study electromagnetic anomaly caused by earthquake and to probe the subsurface resources. The experiment study in Beijing and Tianjin indicated that power spectrum density of SLF signal is bigger than those of natural electromagnetic signal by several times even in the industry noisy area. The apparent resistivity obtained by SLF method has much smaller error bar than those by natural signal and is less influenced by disturbance. An earthquake (M=4.2) occurred near observation site during SLF measurements and coherency between earthquake phenomena and the anomaly of electromagnetic field and apparent resistivity was appeared. It is postulated that the anomaly of electric and magnetic fields and the variation of apparent resistivity were generated due to interaction between regional stress and local electromagnetic source.