Abstract: A shuttle radar topography mission (SRTM) DEM assistant geopositioning method is proposed to solve the problem of geopositioning without ground control points (GCPs) for satellite island and reef images. The method is divided into two stages:coarse and accurate correction. DEM extraction and DEM matching are key steps for both stages, which aim at compensating the relative and absolute errors in triplet image, respectively. In order to fully take advantage of its consistent and stable high precision characteristic of it, SRTM DEM is integrated into the method in each part. In DEM extraction step, it is used to eliminate the sea area and also to determine the vertical search range for solving the land area elevation, so as to avoid the adverse effect of the sea area images and ensure computational efficiency at the same time. As for DEM matching, it is regarded as reference data. Many scenes of Mapping Satellite-1 island and reef images are used to validate the performance of this method. Experimental results show that the method can obtain stable and high geopositioning accuracy for Mapping Satellite-1 island and reef images, regardless of land area proportion or production mode. The planimetric and vertical accuracy are better than 6.2 m and 5.2 m respectively, which can satisfy the accuracy requirements of 1:50 000 scale mapping. The geopositioning accuracy is basically not affected by target DEM resolution, and the computational efficiency depends on proportion of land area and target DEM resolution.