Interferometric Synthetic Aperture Radar is an effective technique to get Digital Elevation Model and ortho-photo map. Layover is one of SAR geometric distortion. The interferometric phase of layover region is not accurate due to the superposition of multi-echo, it makes the discrimination difficult in phase unwrapping. This paper analyzed the SAR image amplitude and interferometric phase characteristic of layover region, based on which an algorithm is present for detecting layover regions. This algorithm can effectively distinguish layover regions and provide reliable basis for InSAR processing. Simulation experiments results show effectiveness of this algorithm.