We bring forward a new method to analyse the sampled chirped fiber grating (SCFG) on the basis of thecoherence theory. With this method , we get more results , not only the characteristics of reflectivity , transmission and time delay about the SCFG, but also the channel’s number , wavelength spacing between two neighboring channels , reflectivity maximum and channel’s bandwidth about the SCFG. This method is more systemic and perfect than the usual transfer matrix method for analysing. And it can guide well for designing and making the SCFG.