Abstract: Distributed optical fiber lines are often exposed to complex terrain conditions and suffer from natural factors such as lightning strike for a long time. In the process of optical fiber signal transmission, with disturbance signal and noise interference, the actual operation state of transmission line cannot be accurately monitored and the fault cannot be accurately located. Aiming at the low accuracy of lightning location in distributed optical network, a new smoothing threshold function is constructed. The threshold function is smooth, continuous and differentiable, which improves the quality of the de manic signal. Through this function, the temperature signal of transmission line monitoring is de-noised by wavelet, the accurate temperature value along the line is obtained, and the fault location is located accurately. The simulation results show that, compared with the traditional threshold function, the smooth threshold function can obtain better de-noising effect, improve the signal-to-noise ratio of the transmission signal, and reduce the root mean square error. The method can improve the detection accuracy of lightning fault location, improve the accuracy of lightning fault removal line and reduce the time of fault location.