To understand the wavelet analysis is put forward from engineering application . The relationship between wavelet function and scale function, the wavelet transfornn and the signal decomposition are given . Furthernnore, we take advantage of the algorit hm of wavelet packet to analyze two ki nds of typical mechanical faults . Results show the wavelet packet is a more efficient method in comparison with windowed fourier transform ( WFT ) and wigner distri - bution (WD) in the field of machinery diagnodis .