A conveyor-driven fabric dyeing machine including an axle distance adjustment device, comprising: a machine body, which has an interior space; one or multiple conveyor devices, which are arranged in the interior space of the machine body, the conveyor device or each of the conveyor devices comprising a conveyor belt in the form of an endless loop, a movable roller arranged at one end of the conveyor belt, and a fixed roller arranged at an opposite end of the conveyor belt, the fixed roller having rotary axles at two ends thereof and having two distal ends respectively coupled through bearings to bearing seats mounted to sidewalls of the machine body, the movable roller having rotary axles at two ends thereof and having two distal ends each of which is respectively coupled through a bearing to a position-adjustable bearing seat, the position-adjustable bearing seat being coupled to a hollow bearing seat base mounted to a side wall of the machine body, wherein the position-adjustable bearing seat is selectively attachable to the hollow bearing seat base at different positions so that the rotary axles of the movable roller are set at different axle distances with respect to the rotary axles of the fixed roller for adjustment of tightness of the conveyor belt, wherein a seal element is provided between contact surfaces of the position-adjustable bearing seat and the hollow bearing seat base in order to provide a sealing effect between the contact surfaces of the position-adjustable bearing seat and the hollow bearing seat base to resist leaking of liquid or pressure, characterized in that the position-adjustable bearing seat is provided with a horizontal rail, and the hollow bearing seat base is provided with a horizontal rail support to ensure a relative movement between them is carried out in a horizontal direction. a machine body, which has an interior space; one or multiple conveyor devices, which are arranged in the interior space of the machine body, the conveyor device or each of the conveyor devices comprising a conveyor belt in the form of an endless loop, a movable roller arranged at one end of the conveyor belt, and a fixed roller arranged at an opposite end of the conveyor belt, the fixed roller having rotary axles at two ends thereof and having two distal ends respectively coupled through bearings to bearing seats mounted to sidewalls of the machine body, the movable roller having rotary axles at two ends thereof and having two distal ends each of which is respectively coupled through a bearing to a position-adjustable bearing seat, the position-adjustable bearing seat being coupled to a hollow bearing seat base mounted to a side wall of the machine body, wherein the position-adjustable bearing seat is selectively attachable to the hollow bearing seat base at different positions so that the rotary axles of the movable roller are set at different axle distances with respect to the rotary axles of the fixed roller for adjustment of tightness of the conveyor belt, wherein a seal element is provided between contact surfaces of the position-adjustable bearing seat and the hollow bearing seat base in order to provide a sealing effect between the contact surfaces of the position-adjustable bearing seat and the hollow bearing seat base to resist leaking of liquid or pressure, characterized in that the position-adjustable bearing seat is provided with a horizontal rail, and the hollow bearing seat base is provided with a horizontal rail support to ensure a relative movement between them is carried out in a horizontal direction.