The invention relates to a processing method for an internal thread core tooth crest arc and a device for realizing the method. The method comprises the following steps: a) mounting an index plate on a middle support plate; b) mounting an electric spindle on the index plate; c) mounting a polishing wheel on the electric spindle; d) clamping a thread core on a spindle chuck in a processing process; e) adjusting the index plate for guaranteeing an inclined angle between the electric spindle and horizontal axis consistent to a helical angle of the internal thread core; f) setting a program and matching the advancing of the support plate with the rotating speed of the spindle chuck, thereby realizing the polishing of the polishing wheel along the internal thread core and then ending. The device comprises the index plate, the middle support plate, the electric spindle, the polishing wheel, the thread core and the spindle chuck, wherein the index plate is arranged on the middle support plate; the electric spindle is adjustably arranged on the index plate; the polishing wheel is arranged at the tail end of the electric spindle; the thread core is arranged on the spindle chuck; the index plate can cause the inclined angle between the electric spindle and horizontal axis be consistent to the helical angle of the internal thread core.