This paper presents a line extraction algorithm in SAR (Synthetic Aperture Radar) images. The algorithm is designed based on the statistical characteristics of the speckle in SAR image. Three steps are involved. Firstly, a new edge detector, which combines the Canny operator and Ratio operator, is used to detect the edge points and calculate their directions, then the edge points are grouped according to their edge direction to form the initial lines. Finally, a high-level grouping step connects the fragmental lines. The proposed new edge operator is CFAR (Constant False Alert Rate) and prevents the line from cleavage. The algorithm has been applied in the X-band airborne SAR images, and the results are presented at the end of this paper.