Aiming at the problem of fault location and signal interference in transmission line, a fault location method of transmission line combining VMD (variational modal decomposition) with soft mathematical morphology was put forward in this paper. Firstly,VMD can decompose noisy signal,and a part of noise is automatically filtered out in the decomposition process; then, the residual interference is further moved by the average flexible morphological filter; finally, the flexible shape edge detection is used to amplify the singular point of the signal, and then the output threshold is set to reduce the influence of the noise background on the abrupt change of the signal. The experimental results show that the proposed method has good noise robustness, suppresses the noise interference and amplifies the traveling wave characteristic signal. It can detect the fault line of the transmission line effectively and obtain higher detection accuracy.