In recent years, quartz crystal sensor has become one of the research focus in the field of biosensor. Its principle is the change characteristics between the quartz crystal and the material on its surface. Based on the principle, the piezoelectric biosensor has the feature of the grade detection capability. The paper sets up a hardware system and analyzes the fundamental frequency signal which the frequency is 10 MHz from QC. By measuring the final frequency of difference signal, the experimental results are obtained. The experimental results show that the frequency fluctuation of the measurement system is less than 10 Hz in the air condition and the frequency fluctuation is less than 30 Hz when the measurement is over.