The invention discloses a drilling jig used for cylinder hole machining. The drilling jig comprises a drilling jig body, a drill bushing, a positioning baffle, a positioning threaded shaft, a base plate and screws, wherein the drilling jig body is provided with a first through hole and a second through hole, a V-shaped groove is formed in one end of the second through hole, and a workpiece is arranged in the second through hole and makes contact with the V-shaped groove; the drill bushing is arranged on the first through hole, the first end of the drill bushing is attached to the upper surface of the drilling jig body, and the second end of the drill bushing makes contact with the V-shaped groove; the positioning baffle is arranged on one side face of the drilling jig body; the positioning threaded shaft is arranged at the first end of the positioning baffle; the base plate is arranged below the workpiece; the screws are arranged at the lower end of the drilling jig body and make contact with the base plate. The V-shaped groove is located above, the workpiece is tightly pushed from bottom to top and arranged in a reversely positioned mode, the workpiece is clamped conveniently, positioning is stable, the holes are in close fit with the workpiece in a non-clearance mode, hole drilling is accurate, machining efficiency is high, machining cost is low, and processes are simple.