Abstract:The instantaneous phase of interference fringe signal sampling point is extracted based on the phase shift principle of Hilbert-transfer, the displacement data is extracted from the phase, and time data is extracted from the sample frequency. We rebuild the free-falling trajectory by means of the least square method, so that the value of g can be calculated. Zero phase-shift low-pass filter is used to remove high frequency noise signal, the polynomial fitting method is used to remove linear interference signal, and data is windowed before fitting to inhibit the Gibbs-phenomenon. The simulation results show that this method can make the g value error under 10-2 μGal. The experimental results obtained mean error of the g value is 0.12 μGal.