In the previous works, the edge-strength function depends on isotropic smoothing of the image, which results in failing to preserve corners and junctions, and may also result in failing to resolve small features that are closely grouped together. In this paper, we present a new interferometric synthetic aperture sonar (InSAS) interferogram filtering method. The presented method, using a modified coupled partial differential equation (PDE) method, has the ability of removing the noise and preserving the edge. Simulated and real data are used to test the presented method. The processing results indicate that the noise is removed effectively, and the image edge is preserved much better than those results given in the literature.