By synthesizing bandwidth in the frequency domain, the distance resolution of Stepped Frequency Radar(SFR) seeker can distinguish the detailed features of complex targets, so as to conduct anti-interference and target identification. When implementing SFR echo simulations, echo model are required to accord with the targets on detailed features, and the target is no longer point target. Nevertheless, using the scattering center extraction means some of the scattering points are discarded and merged, and the detailed description of the target is not accurate. Therefore, a method of generating complex target echo model based on FEKO is proposed, according to the time domain characteristics of the SFR signal, time domain echo model using the scattering data based on FEKO is deduced. In addition, FEKO is utilized to extract the scattering field amplitude and phase information of the target at various incident angles and the information is stored in database. When simulation is implemented, time domain echo calculation is conducted by directly employing stored scattering data, thus high fidelity echo model of complex target can be obtained. This method for echo modeling has practical value in air-to-air missile digital simulation, hardware-in-loop simulation and anti-jamming research.