Abstract: In the application of small sensor and micro-sensor, especially silicon resonant micro-sensor, the detection of weak signals with low SNR(signal noise ratio), the miniaturization and the anti-jamming problems of the self-oscillation closed-loop system are quite outstanding. Digital PLL (phase locked loops) closed loop measurement system of the compound tuning fork resonant pressure sensor directly transforms input analog signals (pressure) into the semi-digital signals (frequency) with high precision, which has basically solved the problems of the measurement system such as micro structure parameters, high work frequency and weak amplitude, strong coupling and big disturbance of the effective signals etc. The method can be applied to the silicon resonant micro-sensor directly, which is significant and directive for the application of silicon resonant microsensors.