A lifting device for a cordless covering, wherein the cordless covering includes a headrail, a bottom rail, and a covering material between the headrail and the bottom rail, the lifting device comprising: a cord reel pivotable on the headrail to rotate in a first direction and in a second direction; a car receivable in the headrail to be moved toward or away from the cord reel; a driving module receivable in the headrail to drive the cord reel to rotate in the first direction, wherein the driving module includes a first reel, a second reel, and a mainspring; a connecting cord having opposite ends connected to the car and the cord reel; and a lifting cord, an end running around the car, and an opposite end extendable out of the headrail to be fastened to the bottom rail, whereby the car moves away from the cord reel to drive the cord reel to rotate in the second direction while the bottom rail is moved away from the headrail; a wheel set receivable in the head rail, wherein the wheel set includes a shaft for the lifting cord to run around; wherein the lifting device for a cordless covering is characterized in that the cord reel has a cone section, and a diameter of the cone section decreases from an end to an opposite end; wherein the connecting cord is reeled in the cone section of the cord reel when the cord reel rotates in the first direction, and the connecting cord is reeled out from the cone section of the cord reel when the cord reel rotates in the second direction, and wherein the first reel is provided with a first gear, the second reel is provided with a second gear, to be meshed with the first gear of the first reel, and the cord reel is provided with a third gear to be meshed with the second gear of the second reel; the mainspring has opposite ends connected to the first reel and the second reel respectively, whereby the mainspring is wound around the first reel or the second reel when the first reel and the second reel rotate in the first direction or in the second direction. a cord reel pivotable on the headrail to rotate in a first direction and in a second direction; a car receivable in the headrail to be moved toward or away from the cord reel; a driving module receivable in the headrail to drive the cord reel to rotate in the first direction, wherein the driving module includes a first reel, a second reel, and a mainspring; a connecting cord having opposite ends connected to the car and the cord reel; and a lifting cord, an end running around the car, and an opposite end extendable out of the headrail to be fastened to the bottom rail, whereby the car moves away from the cord reel to drive the cord reel to rotate in the second direction while the bottom rail is moved away from the headrail; a wheel set receivable in the head rail, wherein the wheel set includes a shaft for the lifting cord to run around; wherein the lifting device for a cordless covering is characterized in that the cord reel has a cone section, and a diameter of the cone section decreases from an end to an opposite end; wherein the connecting cord is reeled in the cone section of the cord reel when the cord reel rotates in the first direction, and the connecting cord is reeled out from the cone section of the cord reel when the cord reel rotates in the second direction, and wherein the first reel is provided with a first gear, the second reel is provided with a second gear, to be meshed with the first gear of the first reel, and the cord reel is provided with a third gear to be meshed with the second gear of the second reel; the mainspring has opposite ends connected to the first reel and the second reel respectively, whereby the mainspring is wound around the first reel or the second reel when the first reel and the second reel rotate in the first direction or in the second direction.