The “black flying” incidents of unmanned aerial vehicles (UAVs) in airports have frequently happened across the country. As the main interference for the detection and identification of UAVs, the characteristics analysis for the echoes of flying birds is of great significance. A fined modeling method of bird echoes is proposed, which considers the actual electromagnetic scattering characteristics. The multi-layer fast multipole method is used to calculate the radar cross section (RCS) of birds in three typical flapping wing attitudes. The flapping wing attitude is calculated and combined with the signal propagation model for the array antenna. Then, the fined modeling of the bird echoes for each channel at any observation point is realized. Experimental results show that the RCS of birds varies greatly with different observation angles. The RCS value corresponding to the side irradiation is higher than that corresponding to the front and back irradiation. The fine modeling of bird echoes can demonstrate the fine description for the bird targets, which can provide the reference to study the echoes of birds.