Abstract: To analyze the dynamic response of the back of AZ31B magnesium alloy sheet to laser shock wave, the laser induced shockwave was measured by PVDF patch sensors and a digital oscilloscope and then piezoelectric waveforms were got. The propagation law of elastic and plastic wave structure was studied combined with shock wave propagation characteristics. The results indicate that the laser induced dynamic response of the material is transient. The time of elastic precursors wave and plastic load wave propagate to the back of the sheet is reflected by the piezoelectric waveforms. Which corresponds to the time of the theory. The waveform amplitude triggered by elastic precursor wave is small while the following plastic load wave causes larger amplitude fluctuations because of its larger energy. The loading process and unloading process of the waves have led to the amplitude increase of the piezoelectric signal.