Abstract: In this paper, according to the influences of the arc weld pool images on the weld forming defects, head, middle and tail of three weld pool partitions were defined.The effect of the arc weld pool image on the forming quality of the weld surface was deeply studied.Through a large number of experiments, the main relationship between the various regions visual characteristics of arc weld pool images and the weld forming defects was obtained.The gray value distribution gradient of three weld pool regions was analyzed by the approximate entropy methed of chaos science.The weld forming quality was correlated positively with the approximate entropy values of regional gray gradient.The bigger the approximate entropy value results in the better forming.The experimental data provides a new quantitative index based on the evaluation of the weld pool image and the control of weld forming quality.