Abstract: A circuit to detect the micro-differential capacitance of micro-silicon inertia sensors was designed,which can be successfully applied in the capacitive MEMS(micro electro mechanical system) accelerometer,especially in the sandwich structure MEMS accelerometers with differential capacitance．The good linearity in large measurement range and high capacitance resolution was achieved by restraining common-mode noise, bias voltage and nonlinearity of voltage output using technologies, such as improving symmetry of rectangle wave source, equi-potential shielding action, coherent demodulation and electrostatic re-balance. The circuit is simple, its linearity, and ability of anti-disturbance are good, and it could be integrated easily. Experiment results show that the measurement range of the accelerometer is ±15g and the capacitance resolution can reach 10^-16F.