Finite elements method（FEM） is performed on the birefringence of side-hole fiber（SHF）.The measurement related with the periodical alternation of the polarization state is introduced to measure the birefringence of SHF

while the reflection spectrum of fiber Bragg grating written in SHF is utilized to analyze the measured birefringence of SHF.The measured result is less than 8 % different from the FEM result

and is accord with the result of spectrum experiment.All results prove that the measurement is reliable and feasible.The measurement proposed possesses the advantages of simpler system

less adjustment and easier to realize

it is a practical method to measure the birefringence of fiber with longer beat-length.