Due to the inherent speckle noise of SAR image and the influence of complicated terrain at the sea-land boundary, it is easy to incorrectly extract the coastline of SAR image by using the region merging method. In order to solve the problem of incorrect segmentation caused by a single scale, an algorithm for coastline segmentation of SAR image based on SLIC super-pixel is proposed.Super-pixel segmentation is used to preprocess the image at first.Then, the improved merging cost based on spectral and texture information (CT-Model) is used to merge, and finally the segmentation results are obtained. The coastline at the sea-land boundary is used for the comparison of segmentation effects. The experimental results show that the improved merging method is more accurate in coastline segmentation than the spectral-histogram method.