The utility model relates to an inner main cover lock screw fixture which is applied to the production of fishing reels and includes a base plate, a workpiece support plate, a pneumatic part and a pressing plate assembly, wherein the pressing plate assembly includes two pressing plates, a support base and a pulling lever; one end of each pressing plate is connected with a pressing plate rubber through a steady pin, the other end of the pressing plate is rotationally connected with the support base through a steady pin, and a cam mechanism is arranged on the pressing plate; the cam mechanism is flexibly connected with the pulling lever; bolt holes are formed in the support base, and the support base is rotationally connected with the pressing plates through the steady pins via the bolt holes; the pulling lever is an H-type sheet body; a connecting part in the middle of the pulling lever is connected with the pneumatic part; the pulling parts at the two ends of the pulling lever are connected with the cam mechanism of one pressing plate. The inner main cover lock screw fixture provided by the utility model is a quick fixture device which is simple in structure, is quick in loosening and clamping, convenient and safe in use, and suitable for mass production.