Abstract: In this paper, a new method converting capacitance to digital has been proposed for MEMS pressure sensor. It is different from traditional way that converting the capacitance to voltage. The weak capacitance signal is converted to the time interval which is quantified by a counter and dealt with the digital filter for high precision capacitance-digital converter. This method is using a simple circuit structure which is less affected by the supply voltage with high linearity and wild input range. Under cadence environment, the circuit is designed and simulated based on TSMC standard BCD 0.25 μm CMOS process model. The circuit's input can range up 8 pF and the resolution is 4 fF.