A flux cored wire 2209 for duplex stainless steel was developed and different weight percent of content of CaF,2, were added in it. The microstructure of slag was observed by Olympus-PMG30 and the gas porosity rate on the weld was tested. The results showed that when the weight percent of CaF,2, were less than 2%,the contents of "FeO" decreased with increasing of the content of CaF,2,which are beneficial to the detachability. If the weight percent of CaF,2, was more than 3%,the detachability of the slag became more compact which could worsen the detachability of slag. In addition,the processing properties become deteriorated. With increasing of the content of CaF,2,the gas porosity reduced.