Abstract: The complex resistivity of frequency electromagnetic sounding contains apparent resistivity of amplitude and phase, the phase can be expressed by the imaginary part and the real part of the complex resistivity can also be obtained through conversion of apparent resistivity of amplitude. This paper focuses on principle and formula which transform the apparent resistivity of amplitude into phase. According to the typical geoelectric model the apparent resistivity of amplitude and phase have been calculated, curve characteristics and the relationship between each other have been analyzed. The results display phase curves with greater amplitude and higher frequency. Therefore, it can improve the stratum resolution and increase the detecting depth. Through explanation combining with the data of apparent resistivity of amplitude and phase, the geological effect of the interpretation can be improved.