Hydrogen diffusion is an important factor that causes additional absorption loss in optical fibers. The concave G.657 fiber with the inner cladding was chosen as the experimental fiber, and the structure and attenuation factors of the G.657 fiber were analyzed. The mechanism of deuterium gas to eliminate the hydrogen sensitivity of the fiber was explained, and the fiber hydrogen diffusion experiment was designed to carry out the deuterium gas treatment formula. By adjusting the two key parameters of deuterium concentration and processing time, the additional attenuation value of the fiber under different experimental conditions was obtained. The comparison experiment results and the tracking retest results show that 0.9% deuterium gas concentration and 80 h deuterium treatment time are suitable for reducing the hydrogen diffusion of G.657 optical fiber.