Abstract: In high-power laser welding process, it is hard to detect weld penetration conditions and back of weld shape directly. The width of back of weld was predicted by the sensing characteristics information of weld face and side surface. Visual sensors are used to capture images which contain weld characteristics information in laser welding process. Weld characteristics are extracted accurately through image segmentation, image hierarchical, pattern recognition and space image process. The extracted characteristics variation trends are corresponding to weld route change obviously. Bayes neural network that contains two hidden layers is established for back of weld width prediction of weldment, and the characteristics extracted from images are used as inputs. The compare results between prediction value and real value verified that the established Bayes neural network has good predictive ability, and better predictive stability even the weld is not ideal.