A successive approximation analog-to-digital converter and conversion method thereof are provided, the successive approximation analog-to-digital converter includes a segmented-multiple-stage capacitor array with redundancy bits, a comparator, a weight-storage circuit, a code reconstruction circuit and a control logic circuit. The successive approximation analog-to-digital converter helps to decrease the complexity of circuit design, featuring small size and low power. Without auxiliary capacitor array, switches and control logic, the circuit can work to precisely measure and correct capacitor mismatch errors.