The liquid dosing system has been studied widely as it had been used in many technical and medical applications. And in recent years, the miniaturization of the liquid dosing system as well as the accuracy of liquid transfer has gradually become a hot research field. In this paper, a MEMS (Micro-electromechanical system) flow sensor was integrated with a PZT(Piezoelectric Transducer) pump to make a closed-loop drug dosing system. Benefiting from the feedback of sensor information, the system can self-adjust the driving voltage of the PZT pump to precisely dispensing desired liquid volume. First, the structure and principle of the PZT pump will be introduced briefly. Secondly, the MEMS flow sensor is presented. Finally, the fuzzy PID (Proportional-Integral-Differential) closed-loop control strategy is proposed to calculate and adjust the driving voltage in real-time. Finally, experiment results show that the drug delivery system could precisely delivery drug volume with error smaller than 0.01µL when desired volume is 100µL.