An electro-optic functional polymer film was prepared by electric-field poling procedures in this study. The I– V (current versus poling voltage) behaviors and the E-O performance of the polymer film were in situ characterized during poling. The vibrational spectroscopy and the Mach–Zehnder interferometer were employed to investigate the dipole orientation behavior and measure the Pockels coefficients of the polymer film. The optical path change, due to the refractive index variation, was found to be critical in determining the Pockels coefficients γ 13 and γ 33, with the Mach–Zehnder interferometer.