A new vibration source number estimation method based on Fast Fourier Transformation (FFT) is proposed. The frequency spectrum characteristic of vibration signals on a machine was analyzed. The characters of the vibration sources were obtained by means of FFT, which was used to estimate the number of vibration sources. The estimations illustrate that the presented method can obtain the correct source number not only under the condition of less source number than that of measurements. The most important is that it can get the source number correctly on the case of more source number than measurements’. The method gives a new idea to estimate the real vibration sources number.