A method and an electronic device for controlling transmission power are provided. The method includes the steps of determining an overlapping level between a channel used by a first wireless module and a channel mask used by a second wireless module; determining whether to adjust the transmission power of the first wireless module according to the overlapping level, wherein the first wireless module complies with a first wireless technology, and the second wireless module complies with a second wireless technology, and the second wireless module is coexistent with the first wireless transmission technology in an overlapping hand.