The utility model discloses a device for cast molding of a basic protective cap. The device comprises four identical casting plates, wherein the four casting plates are connected sequentially; one end of each casting plate is vertically connected with one adjacent casting plate through a connecting piece; the other end of each casting plate is fixedly connected with the other adjacent casting plate through an equilateral chamfering plate. The upper end of each casting plate is slantwise and upwards extended to form a casting eave; reinforcing ribs are respectively welded on outer walls of each two casting plates fixedly connected through the equilateral chamfering plate; the equilateral chamfering plate is arranged on a contact part of each two casting plates vertically connected through the connecting piece; the lower end of each casting plate is outwards extended to form a fixing plate vertical to each casting plate; a plurality of fixing holes are arranged on each fixing plate. The device can meet the requirement of appropriate slope setling of the top surface of the protective cap; is convenient to disassemble, and can protect the surface and the corner angles of the protective cap against damage; meanwhile, the device can meet the requirement of one-time cast molding of the protective cap, and is stable, firm and durable in structure.