The influence of void size, the location of monitoring points and vibration source points on the detection results is very important. Hence, a series of detection tests on concrete decks with defects of various diameters are designed and carried out to simulate and dectete the void condition behind tunnel lining based on the characteristics of impactecho method. In order to explore the possibility and mechanism of detecting lining void by impactecho method, the fast Flourier transform (FFT) method is employed to analyze the vibration acceleration signal; and the characteristics of frequency domain signal from stress wave are studied. The experimental results show that the impactecho method performs well in detection of lining void condition; and the main factors affecting the detection effect include void diameter, arrangement of monitoring points and location of seismic source.