The invention discloses a positioning fixture for machining an inclined surface of a connecting rod, which comprises a positioning pin and a positioning block. A hole positioning mechanism is arranged on the positioning block and used for rotatably positioning the connecting rod in a horizontal plane by the aid of upper surfaces of the positioning pin and the positioning block after being matched with a hole at the head of the connecting rod. When the positioning fixture is used, the surface of the head of the connecting rod contacts with the upper surface of the positioning block, the hole at the head of the connecting rod is matched with the hole positioning mechanism, and the other end of the connecting rod is abutted to the positioning pin, so that the connecting rod is rotatably positioned in the horizontal plane. At the moment, the feed direction of a milling cutter is opposite to the acting force of the positioning pin to the connecting rod, and the milling cutter can be used for milling after tool setting and alignment to machine the needed inclined surface of the connecting rod. The positioning fixture is used for positioning the connecting rod through the positioning pin, the upper surface of the positioning block and the hole positioning mechanism, positioning for the connecting rod is reliable during milling, and the connecting rod is difficult to shift even if the cutting force of the milling cutter to the connecting rod is large, so that machining precision of the inclined surface of the connecting rod is improved.