The application discloses a plastic air pump mechanism, which comprises a plastic body, a plastic output unit and an actuating unit; the plastic body has an integrally forming structure, which comprises a plastic cylinder and a plastic bracket disposed at an air inlet end of the plastic cylinder; the plastic output unit is detachably connected to an air outlet end of the plastic cylinder; the actuating unit comprises a motor, plastic gears disposed on the plastic bracket and electrically connected to the motor, and a plastic rocker arm driven by the plastic gears to realize reciprocating of a piston in the plastic cylinder; and a large body insert of metal is provided in an air outlet of the plastic cylinder. The plastic air pump mechanism can reduce product weight, simplify production and installation processes, save materials and labor costs, and reduce self weight of a vehicle.