Impacting sound analysis is a new method for nuts grading and detection. The acoustic characteristic of the intact and crack hazelnuts is presented in this paper. The gradient accumulation, frequency spectrum and mel-frequency cepstral coefficients (MFCC) were extracted from the impacting sound signals. The results showed that the gradient accumulation parameter was easily calculated, and the accuracy of discriminating crack hazelnuts was about 80%. For frequency spectrum analysis, the spectral distribution of the intact hazelnuts sound concentrates was in 5～8 kHz and that of the crack hazelnuts tends to disperse in wide frequency range. It is difficult to choose the special detection spectrum. The MFCC parameters cannot be used directly. For detection or grading, it should be combined with the statistical models or artificial neural network.