The invention provides an internal main cover lock screw fixture device used in the spinning reel production process. The internal main cover lock screw fixture device comprises a bottom plate, a workpiece supporting plate, a pneumatic part and a pressing plate combination. The pressing plate combination comprises two pressing plates, a supporting base and a shifting lever, one end of each pressing plate is connected with a pressing plate rubber eraser through a fixing pin, the other end of each pressing plate is connected with the supporting base through a fixing pin in a rotating mode, a cam mechanism is further arranged on each pressing plate, and the cam mechanisms are movably connected with the shifting lever; pin insertion holes are formed in the supporting base, and the supporting base is connected with the pressing plates by means of the corresponding fixing fins via the pin insertion holes in a rotating mode; the shifting lever is an H-type sheet, a connecting part in the middle of the shifting lever is connected with the pneumatic part, and shifting parts at the two ends of the shifting lever are connected with the cam mechanisms of the pressing plates. The internal main cover lock screw fixture device is simple in structure, capable of achieving rapid loosening and clamping, convenient and safe to use and suitable for mass production.