The utility model relates to a machining tool, especially it is a spiral type shaping diamond reamer. It includes a non-reaming front guide bar 1, a reaming guide knife 2, and it also includes a non-reaming back guide bar 3. The non-reaming front guide bar 1 is connected with the reaming guide knife 2, which is connected with the non-reaming back guide bar 3, and the three get connection by the same axial lead and they are provided with a continuous spiral groove 5. The reaming guide knife 2 and the outer circumference surface of the rear-half of the non-reaming front guide bar 1 are adhered to the carborundum 6, and the reaming guide knife 2 is provided with a reaming guide angle 4. The bar head of the non-reaming back guide bar 3 is a straight bar, and it is not provided with the spiral groove 5, which is convenient to clamp the clamp; the bar head is also provided with a plug hole 7, which is propitious to rotate a plug hanging knife. The utility model has advantages of through hole quality assurance of processing workpieces, simplification of technological process, production cost decrease and long service life and so on. It is especially suitable for middle, long through holes of processing workpieces.