Abstract: To be dead against the fact that datum of welding structure inspection, such as conformity ratio, first grade conformity ratio, free of defect ratio, overlap each other and cannot give prominence to which is important, the essential component analyzing is used to reduce the vector dimensions and to stand out the main influence factor, with the help of separating a set of vectors into a set of independent ones. The following results can be gotten: The first essential component is conformity and free of defect factor. The bigger the first essential component is,the better the quality of the welding structure will be. The most important factor that influences it is the first grade conformity ratio. Because the losses of information is less than 8% if the first essential component is used to represent the quality of welding structure, it can be used to measure the quality of different part of welding structure, the technical level and quality stability of different working unit. The second essential component is the defect type factor. The smaller the second essential component is, the bigger possibility of the defects belonging to the crack type defect, such as crack, undercut, incomplete penetration etc. will be. Contrarily, the bigger the second essential component, the bigger possibility of the defect belonging to the no crack type defect, like the ball inclusion, ball hole and so on. The losses of information will be less than 1% if both first and second essential component are use to represent the quality of welding structure.

Key words: Defect distinguish, Essential component, Welding quality, Welding structure