The invention provides a roll changing carriage for a steel belt machining line. The roll changing carriage for the steel belt machining line comprises a tackle, a support frame and a gripper device, wherein two guide tracks are arranged on the tackle in parallel in the transverse direction; a first gear sliding track and a first guide groove sliding track are longitudinally arranged at one end of the tackle to form a fixed guide track group which is used for mounting the gripper device; the support frame is slidably mounted on the two guide tracks of the tackle; the support frame comprises an underframe and roll storage racks formed on two sides of the underframe; a second gear sliding track and a second guide groove sliding track are arranged on sides, which are opposite to the two roll storage racks, of the underframe to form a middle guide track group of the support frame; the gripper device comprises a rack and a roll changing gripper mechanism which is mounted on the rack and can slide vertically relative to the rack; and the middle guide track group is aligned to the fixed guide track group by enabling the support frame to slide, so that the gripper device slides into the middle guide track group. The invention further provides a roll changing method of the roll changing carriage. By the roll changing carriage, rolls can be changed quickly, and roll changing efficiency and production efficiency of rolled steel plates are improved.