A double-layer cord rolling device includes a driving unit and a cord rolling unit disposed under the driving unit. The driving unit has an upper base, two upper wheels rotatably disposed on the upper base, and a torsion spring connected with the upper wheels. The cord rolling unit has a lower base, two lower wheels rotatably disposed on the lower base and coaxially mating with the upper wheels, and two transmission cords respectively connected with the lower wheels. One of the upper wheels is connected with one respective lower wheel through a transmission member, thereby rotatable synchronously. As a result, the double-layer cord rolling device of the present invention is shortened in length on the whole without affecting its functioning, thereby attaining the effect of miniaturization.