This paper presents an 11-bit 200MS/s subrange SAR ADC with charge-compensation-based (CCB) reference buffer. The precision, stability and noise of reference voltage are critical to the performance of ADC. Charge is released to or absorbed from reference during data conversion, resulting in fluctuation of reference voltage. Conventionally a large on-chip decoupling capacitor is required to stabilize reference voltage. In this paper, charge losing of reference for a subrange SAR ADC is analyzed, and a charge-compensation-based reference buffer is designed to reduce decoupling capacitor size. The implemented ADC was measured with the charge compensation circuit disabled and enabled, respectively. Measurement results show obvious improvement on SFDR and SNDR with reference charge-compensated