Abstract: A new FFT-based detection algorithm for the existence of synchronization signal in fast frequency-hopping (FFH) system is presented in this paper. Four methods (clipping, envelop-subtraction of two connective hops, iterative double-clipping, clipping-then-subtraction-then-clipping) of evaluating normalized signal to noise ratio(Eb/N0) in frequency domain with jamming are developed and compared. Analysis formulas of these methods are established as well. Our simulations show that numerical results of normalized signal to noise ratio are close to its theoretical analysis for both AWGN and multitone jamming environment, where discrepancy are within the range of ±3 dB. The overall performance of the latter two methods are 5 dB better than the first two methods for partial-band noise jamming. Iterative double-clipping is our recommended approach because of it's low complexity of implementation.