The raw signal simulation of undulate three-dimensional scene is of important significance, because SAR radar platform always flies in three-dimensional scene which has undulate characteristics. A method of the raw signal simulation of undulate three dimensional scene is analysed in this paper. The modeling of undulate three-dimensional scene, the fractal interpolation algorithm of DEM, and the computation of backscatter coefficient using the facet model are expatiated. Also, the influences of particular geometrical distortions and speckles on the echo signal are discussed. In the end the echo signal model is established and the algorithms of its time-domain and frequency-domain are presented. The validity of the method presented in this paper has been verified by simulation experiment of imaging undulate three-dimensional scene.