Abstract: An electric transmission module for window curtains having a winding wheel bridges a power unit and a window curtain set so that the opening/closure of the curtains can be controlled. A string of a set of transmission pieces is wound around a first wheel groove of the winding wheel, and another string of transmission pieces is wound around a second wheel groove of the winding wheel, whereby the forward or backward rotation of the motor urges a synchronic rotation in the winding wheel. The transmission pieces are respectively released at one wheel groove and drawn back at another wheel groove. Compared with the prior art, the transmission module is simple in structure and easy to install. It further improves the problem of sliding between a winding wheel and a transmission string.