Abstract: The midcourse missile imaging method is the key technology for the missile-defense system. Conventional ISAR imaging methods require a uniform function to compensate the phase of the echo. The function is difficult to acquire in the wideband case, so the ISAR imaging result is always smeared. This paper provides a new signal processing algorithm called time-frequency trunk line extraction method. By enhancing the amplitude of the time-frequency doppler which extracted from the narrowband radar return signal, the method improves the doppler imaging resolution effectively. The simulation results and anechoic chamber data of the representative cone-shaped object show that the imaging of the missile target can be obtained from the narrowband radar doppler information using this method.