To point charge, the expression of the induced charge on the electrostatic sensor was calculated. When the point charge moved in the measurement zone, the spatial filtering velocity measuring method was obtained with the amplitude-frequency response of the probe and gate function seemed, and then, in the entire frequency range of speed measurement principle was all effective. The measurement speed expression of spatial filtering method was established with the characteristic frequency of signal spectrum analysis and this method can be used for measuring the flow velocity of the gas-solid two phase flow. The spectral characteristics were obtained with using the transition matrix of the spectral density and analyzing their spectrum segment features of the electrostatic sensor output voltage signal, and then the velocity measurement was completed by finding the characteristic frequency. The flow velocity measurement method was verified by experiment, and the scale factor and the correction factor was calibrated through experiment.