The utility model discloses a down-hole blowout preventer for an oil well. The down-hole blowout preventer for the oil well comprises a piston body, wherein the piston body has a hollow barrel body; sieve holes are formed in the peripheral wall of the piston body; a sealing short piece is correspondingly arranged right below the piston body; a large-diameter cavity and a small-diameter cavity are sequentially formed in the sealing short piece from top to bottom; the inner diameter of the small-diameter cavity is consistent to the outer diameter of the piston body; and the sieve holes in the piston body can be completely blocked by the inner wall of the small-diameter cavity when the piston body completely drops in the small-diameter cavity. A hanging step is formed between the large-diameter cavity and the small-diameter cavity, the upper end of the piston body is connected with an oil outlet cover through an upper joint with threads, an oil outlet is formed in the oil outlet cover, the upper end of the oil outlet cover is connected with an unthreaded rod, the outer diameter of the oil outlet cover is greater than that of the piston body, the oil outlet cover is protruded outwards so as to form a clamping table, and the lower end of the oil outlet cover is hung on the step through the clamping table. By the down-hole blowout preventer for the oil well, large-area pollution can be avoided after the unthreaded rod of a rod pumped well is broken and drops in the well.