Abstract：We systematically summarize the borehole design, electrode placement method, observation method, technical measures, and test indicators of the Tongwei underground resistivity observation system. Using the morphological and the mean square error methods, we compare and analyze the data of the original surface observation system and the new underground observation system and discuss the seismic reflection capability of the downhole observation system. The results show that the downhole observation system can suppress surface electromagnetic interference, significantly improve the signal-to-noise ratio and the dispersion of the data compared with the ground observation system; It also has some ability to reflect the surrounding earthquakes. It can eliminate the influence of changes in shallow surface resistance caused by meteorological factors, improve data stability, and alleviate the contradiction between geoelectric observation land and social economy and urban development. It is an optimal choice to adapt to the development of seismic electromagnetic disciplines under the new situation.