When the silicon resonant pressure micro-sensor works in the self-oscillation close-loop system with thermal-excited and resistor detected, its output has a problem of dreadfully weak signal of micro-sensor. SNR( signal noise ratio) is as low as 10-3, for the system used frequency-equaled signal to excite micro-sensor to get its syntony, as well caused the damaging coupling disturbance. PLL(phase-locked loop) principle and frequency-divided technique were used to design the double closed-loop control circuit of micro-sensor to avoid those. Micro-sensor worked in the outside loop and PLL made the inside loop. The frequency output of micro-sensor had frequency-equaled exciting signal and duple frequency true signal, after multilevel power amplification multiplied duple frequency output of PLL to achieve frequency dividing, adjusting the system state parameters made closed-loop available and phase locking. Results show that the closed-loop system of micro-sensor works effectively based PLL principle and frequency-divided technique and the low SNR gets developed.