To calculate the spectrum of complex structure fiber gratings quickly and effectively is the main basis for analyzing and optimizing the performance of some optical devices,which are composed by superstructure fiber grating,tilted gratings,etc. V-I transter matrix method is proved by the effective index method (EIM) firstly in this paper. The validity of V-I transfer matrix method is analyzed by numerical simulations and experimental results. Compared to the traditional transfer matrix method (TMM),V-I transfer matrix method could greatly improve the efficiency and save the time of calculating N matrixes for analyzing period chirp fiber Bragg gratings (FBG). With the improvement of the precision,the advantage of V-I transfer matrix method will be more apparent.