This study applied the methods of Laplacian Edge Detection (LED) and Bedrock Edge Detection (BED) to Electrical Resistivity Tomography (ERT) data for locating the interfaces of strata. The effectiveness of the two methods was discussed. This study also used numerical forward models of ERT to discuss the influence of the topography effect on locating the interfaces of the strata. The results indicate the BED and LED methods have different suitability for different applications aspects. We performed a field ERT survey at Dong-Shi Forest Farm and the test results were used with the borehole data to increase the interpretation accuracy of the interface locations.