The invention relates to the technical field of petroleum extraction equipment, in particular to a jig frequency reduction device of a pumping unit. The jig frequency reduction device comprises a pumping unit speed reducer, a base, an electromotor, a belt pulley, a bearing and a bearing block. The electromotor, the bearing and the bearing block are installed on the base. The belt pulley comprises a driving wheel arranged on an output shaft of the electromotor, a large intermediate wheel, a small intermediate wheel and a driven wheel. The large intermediate wheel and the small intermediate wheel are arranged on the bearing and the bearing block, and the driven wheel is arranged on the pumping unit speed reducer. The large intermediate wheel and the small intermediate wheel are arranged on one side of the bearing and the bearing block through axles. The driving wheel and the large intermediate wheel are connected through a belt, and the small intermediate wheel and the driven wheel are connected through a belt. The jig frequency reduction device has the advantages that the large intermediate wheel and the small intermediate wheel can be additionally arranged on the existing pumping unit, the jig frequency is reduced, the whole technical scheme is simple, the number of applied parts is small, the structure is reliable, cost is low, an original lean oil well pumping unit intermittent work mode is changed into a continuous low jig frequency work mode, the labor amount of workers is greatly reduced, the jig frequency reduction device is used and popularized in multiple oil field production departments and is very good in repercussion.