The invention provides a compound tool for automobile piston processing. The compound tool is characterized by comprising a tool holder, a blade and a clamping mechanism, wherein the clamping mechanism comprises a clamping part; a bolt hole is formed in the clamping part, and the two ends of the clamping part are separately formed with a contact part and a clamping part; a blocking slot for blocking the blade in the axial direction and a threaded hole for fixing the clamping part are formed in the tool holder; a buckle strip which is matched with the blocking slot is arranged on the blade; theblade is arranged on the end part of the tool holder through the buckle strip so as to form blocking matching with the tool holder; the clamping part is connected on the tool holder through a bolt; and the clamping portion of the clamping part abuts against the blade, and the contact part between the clamping portion and the blade abuts against the end surface of the tool holder. The shape of thecutting edge of the tool is changed, so that simple turning is changed into efficient compound processing; moreover, the shape of the cutting edge of the blade is accurate, so that a product qualification rate is guaranteed; and a buckle structure is adopted on the bottom of the blade, and the blade is perfectly combined with a tool bar, so that the blade is guaranteed to not loosen in a processing process through a buckled combining way.