A charge pump is designed to be capable of quick start up. When the enable signal of the charge pump is arrived, the pump capacitor and the load capacitor of the charge pump can be charged in a short time, referred to as a pre-charging stage. During the normal working period, the pump capacitor and the output capacitor are controlled by the proper switch that is configured into the connection relationship that the charge pump can normally work in order to make the charge pump work normally. As a result of the pre-charge operation, embodiments disclosed herein can reduce the time of the output capacitor for reaching a steady state value.