Nucleic acid amplification has long been used in biosensor technologies, such as DNA sensors, DNA chips and microarrays, due to its advantage of high sensitivity in detecting target DNA. However, dynamic monitoring of nucleic acid amplifications with traditional DNA sensors in real-time is difficult since a constant temperature must be maintained during detection. Thus, the piezoelectric sensor, one type of traditional DNA sensor, is not applicable in real-time monitoring PCR due to the dramatic change in temperature that occurs during reaction. In this study, we introduced strand displacement amplification (SDA), an well-developed nucleic acid amplification technique that can work under conditions of constant temperature, into the development of a novel piezoelectric sensor. Using the new SDA-piezoelectric DNA sensor, we designed a stable system for liquid-phase detection, in which the crystal oscillator plate was fixed by an easily adjustable screw-threaded clamping mechanism and successfully applied the new sensor system to real-time SDA monitoring of human cytomegalovirus (HCMV). This new technique overcomes the shortcomings of traditional DNA sensors in real-time monitoring of nucleic acid amplification. The technique has proved to be a markedly simplified procedure with a number of advantages, such as higher sensitivity, better time efficiency, and the ability of dynamic real-time detection.