Abstract: Following the research of global analysis method of plasma size signals, this paper will, aiming at laser keyhole features when the blowhole defects produced in laser welding, continue to study on the relationship between the blowhole defect and the global analysis model of plasma size signals. And bring out two new feature parameters and their extracting method. The one is base value which represents the intensity of plasma size signals in maximum probability density distribution area, and the other is restless value which describes the level of the signals fluctuation. The relationship of the two feature parameters, real welding conditions and blowhole defects is also researched by experiments, the results showing that the intensity of the base value is closely related to real welding conditions, and the restless value can reflect the blowhole defect situation in laserwelding, moreaccurately.