The method for resistance spot welding quality detection is becoming a serious problem recently. Aluminum alloy has high-conductivity and good thermal conductivity, which affects the stability of welding quality. In this paper, a spot welding monitor system based on magnetic sensor array technique is designed for welding quality detection. And a new signal processing method called the "W-ICA" algorithm is proposed to separate the object signals. The results show that the spot welding monitor system works well. And the modified W-ICA algorithm can extract the mixing signal validly and provide us the original signal information. The extract results of the magnetic sensor array help us to analysis whether the spot quality is good or bad.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.