Abstract: The bolt connection looseness fault seriously affects the normal operation of the iron tower.It is very necessary to detect the bolt connection looseness fault of the iron tower.In this paper, a complete loosening detection method of tower bolts based on wavelet packet energy spectrum is proposed.Firstly, the vibration signals of the transmission tower before and after the bolt is completely loosened are measured by the pulse excitation method, and the vibration signals of the tower component where the excitation point is locatedand the vibration signals of the tower componentwhich was connected by bolt are obtained respectively.Then the wavelet packet is used to decompose the initial signal, the energy spectrum of each frequency band is found out by using the method of energy feature extraction.Finally, the change rule of wavelet packet energy spectrum of the two connected tower materials after the bolts are loosened is given, and the complete looseness detection rules of tower bolts based on wavelet packet energy spectrum is gotten.