Abstract: Flow Electromagnetic Tomography is based on the electrical property differences between oil，gas and water to scan，inverse and show the distribution and condition of multiphase flow.The influence of frequency on it is presented in two ways，electrical properties (conductance and capacitance) and measured values.Through theory and numerical simulation，the discussion on how to choose a proper frequency of the alternating signal is made.The results show that the frequency should be changed according to flow types，when it is between 10kHz and 10MHz，the electrical properties of oil，gas and water can keep steady with remarkable difference.At the same time，both the real parts and the imaginary components of measured valued for every pole are steady with great differences.Hence，the sensors can obtain the highest sensibility.The analysis provides an effective basis for choosing optimal frequency during the actual measurement.

Key words: multiphase flow, imaging well logging, frequency property, electrical property parameter, measured numerical value