The invention relates to a multi-frequency recursive demodulation method for electrical tomographic systems. The method is characterized by comprising the following steps: (1) establishing an original equation and a recursive equation according to m component frequencies of an excitation signal and the sampling frequency of a system; (2) with a zero-phase time of the excitation signal as a starting time, according to data of 2m sampling points a measuring signal, which are closely following the starting time, calculating the initial values of a data matrix B and a state matrix P according to the original equation in the step (1); (3) substituting the initial values and the new sample point data into the recursive equation in the step (1) so as to update B and P; and (4) judging whether a demodulation result meets the accuracy requirements of the system, if so, completing the demodulation operation, and outputting the amplitude values and phase data of m frequency components of the measuring signal; otherwise, returning to the step (3). By using the recursive demodulation method disclosed by the invention, data of at least 2m sampling points is required, and due to the increase of the number of sampling points, the demodulation accuracy and the anti-noise capacity can be improved.