A passive noise shaping SAR ADC circuit was designed in a 65 nm CMOS process. On the basis of SAR ADC, only 6 switches and 2 capacitors were added to the circuit to realize noise shaping, and the whole circuit structure was simple, which could effectively improve the accuracy of SAR ADC. In addition, a passive gain of 2 was achieved, and the noise suppression effect of the comparator was enhanced. The whole loop constructed the noise transfer function with good noise suppression effect, and eliminated the use of residual sampling module and multipath comparator. The simulation results showed that the designed 10-bit noise shaping SAR ADC circuit could reach 124 effective bits and the power consumption was 459 μW under the condition of 33.3 MHz sampling rate, 2.08 MHz bandwidth and 1.2 V input voltage.