The method based on energy deposition to analyze the influence of γ-ray radiation on fiber refractive index was proposed. The fiber dispersion variable which changes with the fiber V parameters and refractive index was analyzed and calculated. The γ radiation effects on fiber dispersion measurement experiments were accomplished, which demonstrates that the γ radiation impact on the presence of fiber dispersion. The fiber dispersion coefficient variation data with radiation dose were obtained. Experimental and theoretical results show that:(1) fiber dispersion coefficient increases with γ radiation dose, within the dose range of(0-500 Gy) fiber dispersion coefficient showed a gradual increase in the amount of saturated trends; (2) changes in the refractive index of the fiber lead to the additional material dispersion. The electron density increases caused by γ radiation is the major factor that results in changes in the refractive index; (3) the decrease of ultra-fast pulsed signal amplitude caused by radiation-induced loss is more significant than pulse broadening caused by radiation-induced dispersion. Both effects exist simultaneously. The pulsed signal distortion is the result of two joint action of especially for long distance optical fiber with nuclear radiation exposure.