The invention discloses a sealing device for a gas-containing coal sample used under triaxial compression experiment conditions. The device comprises an upper compression head, a lower compression head and a coal sample pipe in which coal samples are arranged, wherein the bottom of the upper compression head and the top of the lower compression head block the top and the bottom of the coal sample pipe respectively, the bottom surface of the upper compression head and the top surface of the lower compression head are provided with a perforated plate respectively; each perforated plate is provided with air vents communicated with the coal sample pipe; an upper air duct and a lower air duct are arranged in the upper compression head and the lower compression head respectively; the upper air duct is communicated with the air vents of the perforated plate of the upper compression head; the lower air duct is communicated with the air vents of the perforated plate of the lower compression head; and one plate surface of each perforated plate is provided with a connecting slot by which all air vents in each perforated plate are communicated with one another. The sealing device used can overcome the defects in the prior art and solve the problem that the gas always passes through the coal samples uniformly in a surface contact mode.