Abstract: The anti-jam technique of GPS is researched in the paper, a cascade anti-jam method is proposed, it eliminates narrowband interference in transform domain, and suppresses the residual interference with Cross Spectral Metric method. A common realization of narrowband interference rejection method in transform domain is provided; and the frequency excision algorithm which is the core of transform domain method is proposed. It is proved that if a slice of the received signal spectrum is flat or approximate flat, it is Gaussian distributed, and it can be deduced that the magnitude of spectrum bins is Rayleigh distributed. According to the character, a spectrum slicing method is proposed, which utilizes the statistical property of the flat part of the spectrum to suppress narrowband interference. Through enumerate spacetime methods, it is illuminated that this method consume more resource and has severer distortion than cascade methods proposed in the paper. Simulation indicates that when wideband interference exists, narrowband interference can be detected and eliminated using the proposed method. Through simulation, it is tested that in multiple jam environment, the method has a better anti-jam capability then space-time adaptive processing (STAP) anti-jam method.