Abstract: Dual-channel signal acquisition and characteristic analysis was investigated in pipe MIG welding.Since the echo interference is relatively large in the closed space within pipe, the two-channel arc sound signals were studied with the independent component analysis(ICA).The ICA signals were de-noised with wavelet.The signal-to-noise ratio was obviously improved.The relationship between the arc sound signals inside and outside the pipe and weld penetration status was analyzed from time, frequency and time-frequency domain, respectively.The experimental results showed that the amplitude of signal energy was related to the weld penetration status.The signal energy increased with the increasing of weld penetration.The research in this paper provides technical basis for monitoring welding quality with arc signal.