The utility model discloses an automatic loading and unloading mechanism for a grinder with a cylindrical outer diameter. According to the automatic loading and unloading mechanism, a hopper is arranged on a housing of a grinder body; a trough is formed on the lateral surface of a workbench; a left adjustable support block, a lower support block and a limit baffle piece are adjusted by a workpiece and are arranged at the right end of the workbench; after the pushing quantity of a loading air cylinder is adjusted by the size of the workpiece, the loading air cylinder is arranged at the right end of the workbench and right above a workpiece shaft; an end face support of the workpiece shaft, an exciting coil, an unloading air cylinder and the workpiece shaft are arranged on the same axis; one end of the workpiece shaft is provided with the exciting coil; the end face of the workpiece shaft is supported and arranged on the workpiece shaft, and the other end of the workpiece shaft is provided with the unloading air cylinder; a thimble of the unloading air cylinder penetrates through a central cavity of the workpiece shaft to reach the end face support of the workpiece shaft; and a grinding wheel is arranged at one end of a grinding wheel shaft. The automatic loading and unloading mechanism has the advantages of simple structure, convenience for operation, high machining efficiency and the like, and has great popularization value in the grinding of solid cylinder workpieces.