The utility model discloses an on-line mounting and dismounting device of a foaming gun for a flotation column. The on-line mounting and dismounting device comprises a connecting pipe, a ball valve and a seal cartridge comprising a joint, a gland and circular truncated cones; the inner end of the connecting pipe penetrates through the wall of the flotation column and is welded with the flotation column; the connecting pipe, the ball valve, the joint and the gland cover are sequentially and coaxially connected, and pore passages for mounting the foaming gun are arranged in axial centers of the connecting pipe, the ball valve, the joint and the gland cover; the circular truncated cones are located in an inner hole in a connecting end of the joint and the gland; and a bottleneck-shaped inner hole formed in the axial center of the seal cartridge is used for mounting the foaming gun. The two mounted circular truncated cones form a structure like the shape formed by buckling two bowls, axial movement of two ends of the structure are limited by the joint and the gland respectively, and simultaneously, the bottleneck-shaped pore passage is formed in the axial center of the seal cartridge, so that not only is the foaming gun mounted and dismounted smoothly, but also good positioning and sealing of the mounted foaming gun are guaranteed; and the ball valve is connected between the connecting pipe and the seal cartridge, so that pulp cannot overflow when the foaming gun is replaced, the on-line mounting and dismounting purpose is achieved, the replacement is simple and fast, and the normal production of the flotation column is guaranteed.