The invention relates to a large-caliber optical primary mirror bore finish machining device which comprises a grinding assembly and three groups of optical primary mirror mounting and clamping assemblies, wherein the grinding assembly comprises a connecting body, a rotating assembly, a guide rail mounting plate, a linear guide pair, a grinding head assembly mounting plate, a transmission nut, a transmission lead screw, a grinding head lifting mechanism, a grinding head assembly, a guide rail sealing piece, an adjustment mechanism and a stroke control mechanism; each optical primary mirror mounting and clamping assembly comprises an adjustment screw supporting frame, an adjustment screw, a ball head cap and a ball head cap fixing ring; the grinding assembly has a working mode of being connected to a vertical lifting ram of a large vertical lathe through the connecting body; and the optical primary mirror mounting and clamping assemblies are uniformly fixed on a workbench of the large vertical lathe according to the size of the outer diameter of an optical primary mirror to clamp the excircle of the optical primary mirror. The grinding assembly is convenient to mount and flexibly to adjust the grinding and has simple structure and good practicability. The three groups of the optical primary mirror mounting and clamping assemblies are simultaneously used, and the excircle of the optical primary mirror is aligned by adjusting the adjustment screws, thus the method is simple and easy to apply.