In order to simulate accurately the key parameters of echo signals for missile-borne radar under the condition of spinning, the paper sets up a spinning model during warheads're-entry, and deduces the mathematical expressions of such parameters as time-delay, Doppler frequency and echo power of the beam infinitesimal at a random angle. Finally, the correctness of the model and expressions is proved through simulation. The conclusion of the paper has an important referential significance for the accurate simulation of wide-beam radar echo in the future.