In order to solve the problem that the backscattered signal is seriousl y disturbed by noise in an optical time domain reflectometer (OTDR),this work proposes an O TDR signal denoising algorithm based on complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) improved wavelet threshold.By using the CEEMDAN decomposition algorithm to resist modal aliasing and reduce reconstructi on errors,the signal is decomposed into several intrinsic mode function (IMF) components.On the basis of th e analysis method of the correlation coefficient,the critical point between the noise-dom inated IMF components and the signal-dominated IMF components is found,and the noise-dom inated IMF components are removed.Then the signal-dominated IMF components are denois ed by the improved wavelet threshold denoising method,and the signal is finally recon structed.The results show that the proposed method can suppress the noise better and achieve better results and highlight the event featu res compared with the traditional hard threshold method, CEEMDAN-hard threshold method and the improved wavelet threshold method and make event detection easier.