Differential pulse width modulation circuit is the use of charging and discharging of the sensor capacitance circuit output pulse width varies with the sensor capacitance change. Capacitive sensor is a device of the electric capacity change measured, and it is a variable capacitor, and then the voltage is obtained by measuring circuit, and the relationship between voltage and displacement are derived and realize the displacement measurement. The paper proposes design of capacitive displacement sensor and measuring circuit based on modulated differential pulse width. Through the experimental analysis of error causes, and put forward measures to improve the precision of measuring circui