A duet power-driven window shade comprises a controlling device to receive an external controlling signal, which is then analyzed, determined and compared with a preset value in a memory unit of the controlling device. A driving signal is output via a processing unit according to a comparing result. A power source then brings convolutions of a first covering sheet and a second covering sheet in sequence or concurrently for increasing the rolling speed and the using convenience and allowing the connecting members connected to the covering sheets to be efficiently rolled up without entanglement so that the duet power-driven window shade is smoothly operated.