Abstract: A DEM reconstruction method based on CSSM(coherent signal subspace method)is proposed for multi-frequence InSAR systems.This method transforms the correlation matrices at many frequency bins into one general correlation matrix at one focusing frequencyusing a transformation matrix(focusing matrix),then estimates the elevation using subspace projecting method.The method can provide more accurate estimation of the height even when the coregistration error reaches one pixel than previous methods.The effectiveness and robustness of the method is verified by simulated data and SIR-C real data.