The speckle effect inevitably exists in the image of the Synthetic Aperture Radar (SAR). The removal of the speckle noise is the necessary approach before automatic partition, classification, target detection and abstraction of other quantitative special information in the SAR image, so it is very meaningful to eliminate or furthest restrain the speckle noises when the spatial resolution of the image is not be reduced. In this paper, the FIR filter is used to remove the noise in the SAR image, and optimal filtering coefficient is selected through experiment and analysis in the filtering process. The results show that the FIR filter used to remove noises in the SAR image is better than other traditional filtering methods in keeping the radiolocation feature and restraining the speckle noises, and the filtering speed is quicker. At the same time, the selection of the filtering coefficient will largely influence the de-noising effect of the FIR filter.