Localization of loose parts is a crucial technique of a loose parts monitoring system for nuclear power plants. Accurate localization is beneficial for fault diagnosis and the continuous tracking of loose parts. Combined with time-frequency signal-processing methods, this paper presents a loose parts localization delay calculation method based on the continuous wavelet transform (CWT) and Hilbert envelope. First, it is identified that the signal is processed by CWT; second, the arrival time of the signal is determined by the Hilbert envelope method; and third, the grid localization method is applied to realize localization. This method, which uses the main frequency band of the impact signal as the Hilbert envelope localization signal, can minimize the effect of changes in the group velocity on time delay, and the Hilbert transform can obtain more accurate time delays. The experimental results show that this loose parts localization delay calculation based on the CWT and Hilbert envelope method has strong anti-interference capacity and high locating precision.