Abstract: The spatter formation mechanism of self-shielded flux cored wire has a remarkable different with other welding materials because of its speciality in wire's construction and welding method.The mechanism and influencing factors of welding spatter are studied.High-speed photographs indicate that there are mainly three types of spatter in self-shielded flux cored arc welding, which are big spatter caused by arc force, bubble released spatter and gas explosion spatter.Five flux ingredients, which influence the welding spatter greatly, are investigated by means of spatter tests using mixing material regression method.Experimental result shows that the effect of fluorides and carbonates is greater than that of oxides, killing agents and alloys.