A soft-start circuit is provided. The soft-start circuit comprises: an input stage, a pump stage, a second resistor and a capacitor. The input stage comprises a first resistor to receive an input voltage to provide a reference current at a first node. The pump stage comprises N current branches connected in parallel each comprising a current source connected to the first node and a switch to transfer the current from the current source to the second node while the switch operates in a connecting state. The switches has 2N connecting modes performed one after another to generate an output current with a gradual increment output current at the second node with 2N current levels; and the second resistor and the capacitor are connected in parallel between the second node and the ground potential to generate an output voltage with a gradual increment with 2N voltage levels according to output current.