A power management method is suitable for an electronic device including a controller, a processor and a battery, and includes following steps. A first power is provided to the electronic device by a power adapter, and a maximum value of the first power is smaller than a maximum value of a rated consumed power of the electronic device. A power state of a second power of the battery is obtained by the controller. A control signal is generated according to the power state, and the processor adjusts an operation performance of the processor based on the control signal. The operation performance of the processor is continuously adjusted according to the power state.