Abstract: An experimental study of the radar cross section in a helicopter inlet syncretized with engine cabin was completed in different polarization ways,terminals,attack angles and azimuth. Meanwhile,the RCS characteristics were also analyzed at various states.The results indicate that RCS of this inlet is lower in vertical polarization way than that in horizontal polarization way,and higher in plate terminal than in blade terminal.The radar cross section at nearly sideslip is larger than that at front flight and nearly backward flying.In the experiments of different attack angles (-10°,-5°,0°,5°,10°),the RCS at 10° is relatively low,and at -5° is relatively high.