Abstract: The hidden roadway of small coal kiln with shallow buried depth under expressway is a hidden danger of roadbed safety. It is easy to detect the original stratum, but it is difficult to detect the roadway of small coal kiln under the stone roadbed filled with stone. In view of this situation, high-density resistivity method is used to detect the local area of Tongchuan section of G65 expressway. Electrodes are arranged in the way of small polar distance, shallow drilling and grouting cement slurry for data acquisition. Weighted average interpolation method is used to eliminate the influence of inhomogeneous stone layers on data in the data pretreatment stage, and then least square inversion with smooth restriction conditions is carried out to obtain the known data of abnormal characteristics of water-accumulated roadway in small coal kiln. According to this method, all the data in the exploration section are processed, and three abnormal areas are found, which have been verified by drilling.