Aimed at the segmentation between the sea and the land in remote sensing images and the question of the extraction of the coastline, a new method is proposed. Firstly, the existed methods are analyzed and the limitations and shortcomings are determined. Then the most basic methods are adopted such as threshold segmentation and edge detection technology. Enlightened by the basic method, an edge-search method and a threshold segmentation method are proposed. Experimental results show that they are effective on segmentation between the sea and the land and the extraction of the coastline. Finally, segmentation between the sea and the land and the extraction of the coastline are realized.