According to helium-arc welding characteristics of 2219 aluminum alloy，a real-time visual sensingsystem for welding process was constructed，a clear image of the molten pool was obtained. In order to obtain the sizeparameters of 2219 aluminum alloy helium arc welding pool and to analyze the characteristics of the molten pool，morphological algorithm was adopted. The edge shape of typical molten pool image was extracted and the characteristic dimension of width of molten pool was obtained. The results show that the width feature of the extracted image can reflect the weld size information accurately. The morphological algorithm has high accuracy and fast calculation speed，which can meet the real-time image processing requirements of 2219 aluminum alloy helium arc welding pool.However，different thresholds and structural elements have great influence on image feature extraction.The threshold adaptive algorithm can meet the complex requirements of real-time visual monitoring of weld pool characteristics in engineering.system for welding process was constructed，a clear image of the molten pool was obtained. In order to obtain the sizeparameters of 2219 aluminum alloy helium arc welding pool and to analyze the characteristics of the molten pool，morphological algorithm was adopted. The edge shape of typical molten pool image was extracted and the characteristic dimension of width of molten pool was obtained. The results show that the width feature of the extracted image can reflect the weld size information accurately. The morphological algorithm has high accuracy and fast calculation speed，which can meet the real-time image processing requirements of 2219 aluminum alloy helium arc welding pool.However，different thresholds and structural elements have great influence on image feature extraction.The threshold adaptive algorithm can meet the complex requirements of real-time visual monitoring of weld pool characteristics in engineering.