An electronic cigarette and a method for supplying a constant power therein, the electronic cigarette comprises an atomizer with a heating wire. The electronic cigarette also comprises a power supply module for supplying power to the heating wire to heat the heating wire, and further comprises a microprocessor, a detecting module connected to the microprocessor, and a voltage adjusting module. A preset constant power can supply to the heating wire of the atomizer in the electronic cigarette, so that a consistent heating power can be applied to each of the electronic cigarettes produced in batch production, and smoke amount and flavor of each of the electronic cigarettes are more consistent, thereby better meeting demands of consumers.