SAR simulation technology is of great significance for the development of synthetic aperture radar. The paper firstly proposes the constituted principles of missile SAR echo simulation system, discusses and establishes mathematical model of the Missile SAR echo signal, and describes the target Scattering model and the geometric model on the distributed targets and described the target Scattering model and the geometric model on the distributed targets, and finally provides a theoretical basis for further study the simulation of missile-borne SAR echo system.