A charge-redistribution successive approximation ADC includes: a comparator, generating a comparison result; a register, storing a digital output code, determining a bit value of the digital output code according to the comparison value; a control unit, generating a control signal according to the digital output code; a plurality of first capacitors, each including a first end and a second end, the first end coupled to a first input end of the comparator; at least one second capacitor, including a third end and a fourth end, the third end coupled to the first input end of the comparator. Before the voltages of the second end of each first capacitor and the fourth end of the second capacitor are switched, the second end is coupled to a first voltage and the fourth end is coupled to a second voltage different from the first voltage.