Engine cylinder bonnet bolt thermal treatment straightness accuracy protection device, by grab, go up spreader, cylinder bolt, go up the perforated plate, the stand, down the spreader, perforated plate, tightening nut, fender bracket are constituteed down. The fender bracket comprises four stands that stand vertically, and the upper portion of stand transversely is provided with four and goes up spreaders, and the lower part of stand 5 transversely is provided with four lower spreaders, the perforated plate is installed on the upper portion of fender bracket, goes up the higher authority that the spreader was arranged in to the perforated plate, the perforated plate is installed down to the lower part of fender bracket, and the higher authority of spreader is arranged down in to lower perforated plate, the cylinder bolt passes the perforated plate and the lower through -hole of perforated plate, and the tightening nut is installed to the lower extreme of cylinder bolt, the outside of protection is installed and is grabbed the handle. The utility model has the advantages of: avoid the cylinder bolt to appear owing to move colliding and the damage problem in heat treatment process, produced crooked possibility when having avoided temperature rising or decline, guaranteed the straightness accuracy of cylinder bolt.