This paper proposes a blind narrowband interference suppression algorithm based on FFT. By keeping the phase spectrum of the received signal and hard limiting the magnitude spectrum, the signal is reconstructed with the stored phase spectrum and limited magnitude spectrum. During the process, the power of NBIs is greatly decreased, thus the suppression of the NBIs is achieved. The method can be used to suppress various NBIs. The algorithm has a very low complexity that is very suitable to the real-time processing