Due to the great success of MEMS based FBARs in wireless communication, advantages of being thin, small size, compatible with the IC and much higher resonant frequency and more sensitive than traditional micro mass sensor like quartz crystal microbalance(QCM ), which have led to further applications as microbial molecular detection sensor in biological and biomedical fields. Most of microbial molecules survive in liquid environment, however, the acoustic loss of the longitudinal wave mode FBAR is larger in liquid environment, Q value is around 3.53. A new compressional wave mode FBAR micro mass sensor used in liquid environment is present. After analyzing characteristics of longitudinal wave mode FBAR in gas and liquid phase environments, the sensor is designed by embedding a micro fluidic channel on the top of the FBAR to solve the problem of low Q. Simulation shows the new Q value increases to 30.85 which increased by almost 9 times. This advantage can greatly enhance the performance of the sensor for microbial molecular detection.