A switch power supply having active power factor correction is provided, including a power factor correction (PFC) circuit, a filter circuit, a main power stage, a first capacitor and an indicating circuit. The indicating circuit consists of a light emitting diode (LED) and an inductor; and the current direction of power supplied from the PFC circuit to the main power stage through the inductor is opposite to the conduction direction of the LED. The filter circuit at least comprises an electrolytic capacitor. When the electrolytic capacitor is normal, the LED does not emit light. When the equivalent series resistance (ESR) of the electrolytic capacitor sharply rises, the exciting current appears in the inductor. When a power transistor in the main power stage is switched off, the exciting current passes through the LED for freewheeling and enables the LED to emit light.