A detection circuit for measuring micro differential capacitor comprises a frequency selection circuit, a phase-locked loop tracking circuit, a logic gating circuit and a low-pass filtering circuit, wherein the frequency selection circuit and the phase-locked loop tracking circuit are formed into resonance units; the resonance frequency of each resonance unit is determined by the capacity of a to-be-measured differential capacitor; and two sets of resonance units formed by the differential capacitor can realize frequency output in direct proportion to the capacity of the differential capacitorunder the action of a back-end logic gating circuit and the low-pass filtering circuit. The detection circuit has high detection precision and output linearity, small temperature drift and strong anti-interference capacity; moreover, the detection circuit has simple circuit structure and is convenient for engineering and integrated circuit making. The detection circuit is suitable for the measurement based on micro differential capacitor sensitive mechanism in the fields of medical apparatus, security-monitoring detection, inertia device and fluid characteristics measurement.