1. A defect detection method for detecting a crystalline silicon product, comprising the steps of: (a) enabling, in a non-contact manner, the crystalline silicon product to generate micro-vibration, so as to generate an excitation signal; (b) acquiring the excitation signal generated from the crystalline silicon product by using an acquisition device; and (c) performing a time-frequency analysis with respect to the acquired excitation signal, so as to generate an analysis result, wherein step (a) enables the crystalline silicon product to generate more than once micro-vibrations with different directions in a predetermined time by changing direction of the crystalline silicon product, so as to enable the crystalline silicon product to generate the excitation signal in the predetermined time, and step (a) enables the crystalline silicon product to generate the more than once micro-vibrations at a side surface thereof.