Using COMSOL, the mechanical model of ceramic products detection by coin-tap sound is constructed to predict the maximum impact force in the impact dynamic quantity. The ceramic structure is simplified as a cube ceramic test piece, and its stress signal is analyzed in time domain. The difference of the impact signal waveform of the cointap sound between qualified ceramics and defective ceramics, as well as the response difference of the size of the defect to the percussion impact force, are studied. The results show that the peak value of impact force signal of qualified ceramics is higher than that of defective ceramics. The width and length of the defect affect the amplitude of the impact force signal. The wider the defect width or the longer the defect length, the lower the peak value of the impact force signal. When the defect depth is small, the influence on the peak value of impact force signal is not obvious. The research results reveal the difference in the response characteristics of qualified ceramics and defective ceramics to impact force, which can provide an effective theoretical support for the accurate identification of defective ceramics in the online detection process of automatic production line.