An oil pumping unit with pinion reciprocating on rack has a base, a housing, crown block, a steel wire rope, a motor, a reducer, a pinion, and a rack. Rack seats are fixed on the inner sides of the front portion of the housing and the rack is secured on the rack seats. The two inner sides of the housing are guiding rails for the reciprocating frame. At each of the four corners of the reciprocating frame, a horizontal guiding wheel and a longitudinal guiding wheel are mounted, connecting to a pendulous frame via a hinge. The rear interior portion of the housing has a power cable box mounted, in the middle of which is an opening. Shelves are mounted on the upper portion of the housing. The steel wire rope (5) passes through the shelves.