Abstract: High density electrical method and seismic imaging method are adopted to detect the mined-out areas in the Gongchangling opencut iron mine in Liaoning Province. The high density electrical survey may reveal the mined-out area, but it is often interfered by the electric field in the mining area. The seismic imaging method is quick in data collecting and processing, with ability of anti-interference and without limitation of detecting depth. It can infer the buried depth of abnormal based on the waveform features and the morphology of isophased axis. The two techniques should aid and verify each other.