As an important electromagnetic surveying method, Controlled Source Audio Frequency Magnetotelluric (CSAMT) method is operated within a very broad bandwidth, so observational data is vulnerable to varies noise. To solve this problem, real-time data processing method for CSAMT was studied is this paper. The frequency table design method, all-phase analysis, and the judgment and elimination of abnormal value were discussed. Cagniard resistivity and phase measurement under strong disturbances was achieved by integrated utilization of multiple error inspection method as well as anomalous extremum value identification method. Field tests confirmed that the data processing method described in this paper can extract effective Cagnia apparent resistivity and impedance phase from the original data with very low SNR, helping to improve the anti-interference capability and expand the application scope of CSAMT.