A triple layer folding door includes an inner layer door, an outer layer door, a middle layer door provided therebetween, and a sliding arrangement, which comprises: a left and right pulley mounted on a both end portion of the middle layer door respectively, a left belt winding on the left pulley, wherein a first end of the left belt extending to the right end portion of the inner layer door from the left pulley and a second end of the left belt extending to the right end portion of the outer layer door from the left pulley, and a right belt winding on the right pulley, wherein a first end of the right belt extending to the left end portion of the inner layer door and a second end of the right belt extending to the left end portion of the outer layer door.