An axle distance adjustment device is provided for a conveyor-driven fabric dyeing machine M and includes a conveyor belt 11 in the form of an endless loop arranged inside a machine body 1 and a fixed roller 12B and a movable roller 12A respectively arranged at two ends of the conveyor belt 11. The fixed roller 12B has a rotary axle 122 having two ends mounted through bearings to bearing seats mounted on sidewalls of the machine body 1. The movable roller 12A has a rotary axle 121 having two ends mounted through bearings to position-adjustable bearing seats 31, which are coupled to hollow bearing seat bases 32 mounted to the sidewalls of the machine body 1. The position-adjustable bearing seats 31 are attachable to the hollow bearing seat bases 32 at different locations so that an axle distance between the rotary axle 122 of the fixed roller 12B and the rotary axle 121 of the movable roller 12A is changed for adjustment of tightness of the conveyor belt 11.