The effects of the tapering region length and shape on the spectral characteristics of the biconical fiber Bragg grating (FBG) are analyze d using transfer matrix method.The simulation results show that with the increase of the length of the tapering region,the se condary peak amplitudes between the two main peaks increase in different proportions,and there is a larger prop ortion in the middle part.When the tapering region length increases by an order of magnitude,the middle peaks have an obvious series trend.With the length increases,the middle peaks fully connect together,and the two main peak s impolitely change.When the tapering region is a linear and exponential shape,the optical spectrum of the bi conical FBG is almost the same,and when the tapering region is a parabolic shape,the secondary peaks shift to th e right side of the main peak,and the amplitude of the peak decreases gradually.