The utility model discloses a self-forming baffle and a reactive foam sealing device thereof, and comprises a sealing baffle; the sealing baffle is designed into an elastic expansion bag capable of expanding in a radial direction to form the self-forming baffle; the elastic expansion bag is provided with an injection port for injecting reactive foam mixture; through the foaming, the expansion and the curing of reactive foam in the baffle, an irregular surface of the inner wall of a coal seam can be self-adapted to, and a good sealed area is formed between a gas drainage pipe and a coal seam drill hole; through the self-forming baffle, at least two self-forming baffles are arranged at any positions in a gas drainage hole, and consequently, a sealed space can be formed among the inside of the coal seam drill hole, the outer wall of the gas drainage pipe and the self-forming baffles; and the reactive foam is poured into the sealed space, so that the reactive foam is restricted and foams, the foam quality is improved, and the sealing quality is improved.