Abstract: In the past ten or twenty years, more and more geo-resistivity observation stations are being faced with increasingly electromagnetic interference, such as subway and rail traffic system in urban area, which seriously affects the quality of observation data. The AC geo-resistivity observation method has been found to be effective to solve this problem and can be used for earthquake monitoring and prediction. This paper introduced firstly the theory of the AC observation method, and then three different signal detection methods, i.e., the digital filter method, the spectrum analysis method and the correlation detection method, are used in the simulation. The analysis results are obtained by simulating an actual work process of AC geo-resistivity observation method. Comparison of the relative error and relative standard deviation on the condition of different signal-noise ratio, sampling rate or sampling time shows that frequency spectra method can be taken as the best method for the signal observation, providing theoretical basis for developing the AC geo-resistivity observation system.