An SAR ADC capable of reducing energy consumption, including a voltage selecting circuit for configuring a capacitor circuit to form a first equivalent capacitor having a capacitance of (2m−1)C, a second equivalent capacitor having a capacitance of (2n−2m−1)C, a fourth equivalent capacitor having a capacitance of (2m−1)C, and a fifth equivalent capacitor having a capacitance of (2n−2m−1)C, wherein, the first equivalent capacitor has one terminal coupled to a reference voltage or a ground voltage, and the other terminal coupled to a positive input end of a comparator; the second equivalent capacitor is coupled between a common mode voltage and the positive input end; the fourth equivalent capacitor has one terminal coupled to the ground voltage or the reference voltage, and the other terminal coupled to a negative input end of the comparator; and the fifth equivalent capacitor is coupled between the common mode voltage and the negative input end.