Abstract: In order to study the effects of storage time on acoustic properties of watermelons， the changes of vibration response frequency of watermelon were studied by the way of percussion with the vibration detection system designed by our lab. The results showed that the first response fundamental frequency had a good correlation with storage time， and then a nonlinear function model was established， the correlation coefficient was 0.919 1. By selecting multiple vibration eigenvalues， a multiple linear regression model was established to describe storage time. Test analysis of the watermelon samples showed that it could get the best measurement model when placing the excitation and receiving points at the watermelons stem and stalk， respectively. The correlation coefficient and standard estimation error of this model was 0.931 3 and 1.8120， respectively. It provided a reference for the storage and sale of watermelon after picking.

Key words: watermelon, tapping vibration, storage time, multiple linear regression