The invention discloses a machining technology for a lengthened milling cutter. The machining technology is characterized by comprising the following steps that firstly, steel banks are subjected to outer circle polishing, heat treatment, acid pickling, drying and groove cutting to be made into a lengthened milling cutter blank and a lengthened cutter handle blank; secondly, by mass, 3.5 parts of diethanol amine, 2.5 parts of polyacrylamide, 0.8 part of borate and 1.7 parts of polyvinyl butyral resin are added into 12.5 parts of deionized water, the mixture is stirred and mixed fully, then 1.3 parts of boric acid, 2.6 parts of hydroxyethyl cellulose and 2.9 parts of oleamide are added in sequence, the mixture is fully stirred and mixed, and a grinding and cutting working solution is obtained; thirdly, the milling cutter blank is ground and cut, wherein the grinding and cutting working solution is used in the grinding and cutting process; fourthly, light wave heating is carried out, and heat stress is eliminated; fifthly, a machined lengthened milling cutter and a machined lengthened cutter handle are welded together. According to the preparing method for the spiral milling cutter, the prepared milling cutter has high surface quality and is long in service life.