There are a lot of high-frequency noises in the ocean gravity measurement data, so it is necessary to use a low-pass filter to extract the actual gravity anomaly information. Combined with the measured ocean gravity data, the method of determining the cut-off frequency and length of the low-pass filter is investigated, and the FIR low-pass filters with different window functions are designed. The experimental results of marine gravimetric data processing show that both the coincidence accuracy in the repeating line and error in the intersection non-conformity value of the FIR low-pass filter processing of Hanning window and Hamming window are better than 0.5 mGal(1 Gal=10-2 m/s2）, which can meet the requirements of marine gravity measurement.