Abstract: Proper selection and setting of major technological parameters for HF weld tube manufacture is very criticalto ensure consistent operation and product quality and enhancement of productivity. All described here are details about the formation and morphology (mainly the seam) of the metal flow line of HF weld tube, and analysis concerning defects and bad morphology frequently identified in fusion line, heat-affecting area and metal flow line, and the causes therefor and negative influence on tube quality thereby. In addition, operation procedure for analysis of the metal flow line is introduced.