Abstract: In this paper,the cause for the fluctuation of high strength weld metals in toughness is analyzed by mathematical statistics and regression method.The results indicate that for the same batch material,weld metals toughness fluctuats in compliance with normal distribution function,whose dispersive characteristic is related to different weld metal cooling rate induced by inconsistent welding conditions,and for the different batch materials,weld metals toughness fluctuats depending on its sulfur and phosphorus contents.Therefore it is necessary to control welding conditions and impurity content in weld materials to ensure tough weld joints in a practice.