The invention provides an inner gear machining method and a special gear shaping clamp. The processing method comprises the following steps: firstly carrying out rough machining on wheel teeth by virtue of the common shaping machine, adopting an indexing mechanism and a shaping tool with a trapezoidal cutting edge to machine gear grooves in a one-by-one manner, obtaining a trapezoidal middle tooth profile which is very close to the final tooth profile of an inner gear, and remaining a small amount of fine-machined allowance; and then adopting the shaping tool with a conjugate tooth profile on the gear shaping machine to carry out fine machining on the wheel teeth. The special gear shaping clamp comprises a base, pressing plates, an adjusting screw, a screw, a pressing nut, a steel ball, a retaining frame, a sliding block, sliding block bolts, sliding block nuts, a positioning rod and a positioning pin, and the special gear shaping clamp has the main functions of aligning the peripheral positions of the inner gear and the gear shaping tool and clamping a workpiece. In the inner gear machined by adopting the method, the gear shaping efficiency can be effectively improved, the wear of the gear shaping tool can be reduced and the machining accuracy of the wheel tooth can be improved.