The spectral property of super structured fiber grating was analyzed with Fourier transposition. It′s conclusion was then compared with the results gotten form the deduction with coupled mode theory. The two outcomes were unified with each other in many aspects, when reflective ratio was low enough. Furthermore, it is found that the interval Δ λ between two reflective peaks of sample fiber grating was related not only to the period p of grating, but also closely to sampling rate T. The result has already been proved by experiment.