The invention relates to a floating mechanism used for supporting a floating part. The floating mechanism at least comprises three lever groups and radial pulley blocks, the quantity of which is equal to that of the levers and the radial pulley blocks are not on the same straight line, wherein each lever group comprises two levers sharing the same fulcrum arranged at one end of each lever, and the other end of each lever is connected with one end of a horizontally arranged spring; and the other end of the spring is connected on a worktable or a rail. The radial pulley blocks comprise radial pulleys and pulley supporting seats on which the fulcrums are installed, and the rotary axes of the radial pulleys are perpendicular to the axes of the fulcrums. The invention also provides a sealing device for the end part of an annular air channel so as to guarantee the sealing of the end part of the annular air channel.