With regard to the feature that the vertical precision of SRTM(shuttle radar topography mission)data in the flat terrain area is much higher than its nominal precision, it is proposed that a stereo block adjustment algorithm without ground control by adopting SRTM data as elevation constraint. In order to improve overall vertical accuracy of the image, by constructing a wide local area network and setting intensive connecting points, SRTM is set as the initial vertical value of connecting points. In the process of adjustment calculation, ground height of connecting points distributing in the flat terrain area is made sure to rigorously approach to vertical accuracy of SRTM. Through the experiment employing ZY-3 triple linear array stereo satellite images cover across all of Hubei province, the verification results prove that the method is effective. The height root mean square errors(RMSEs)of ZY-3 stereo images is improved from 7.2 m to 2.0 m without ground control, and the RMSEs of flat areas and mountain areas improved to 1.44 m and 3.0 m respectively, which fulfills the elevation accuracy requirement of national 1:25 000 scale mapping applications.