The invention discloses a large cast stainless steel wing cabin fusion cabin section machining method, and belongs to the field of aerospace manufacturing. The machining method solves the problems that according to an existing wing cabin fusion cabin section machining method, clamping and alignment are difficult, the efficiency during machining is low, machining is prone to deformation, the production efficiency is low, and the machining precision consistency is difficult to guarantee. According to the process scheme of the machining method, the method comprises the steps of material preparation, three-dimensional scanning, scribing, benchmark rough machining, shape inner cavity rough machining, inspection, aging treatment, three-dimensional scanning, shape inner cavity semi-finish machining, inspection, aging treatment, inspection, shape finish machining, inner cavity finish machining, high-precision boring, fluorescence detection, finished product inspection and warehousing. According to the machining method, machining is carried out on a wing cabin fusion cabin section, the shape machining efficiency and machining stability of the wing cabin fusion cabin section are effectivelyimproved, and meanwhile the product quality is guaranteed.