The utility model relates to a leading-down pitch adjusting and fastening device used for a composite optical cable terminal of an overhead ground wire in a transformer station of an electric power system. The device is characterized in that an optical cable fixing clamp and an anti-creepage insulator are fixed on a pitch pillar; the pitch pillar is fixed on an upper pitch adjusting arm; and a pitch connection hoop is fixed on a lower pitch adjusting arm. The beneficial effects of the utility model reside in that the device is convenient for pitch adjusting and is rapid and reliable to mount; the mounting work efficiency of the field on-pole work is increased; the problem of detachment of an optical cable due to aging of an original rubber gasket is solved; the device ensures that the leading-down optical cable in the transformer station cannot discharge to a rod frame and cannot generate strand breakage; the safe operation rate of the leading-down cable in the transformer station is increased; and the operation cost of a power supply enterprise is lowered.