Abstract: The metallurgical mechanism of inclusion forming in droplet metal,which weld was in arc weling with two kinds of oxide slag system sintered fluxes self-made in laboratory,was studied.With the rapidly extracted droplet metal experimental method designed,the oxygen content of droplet metal taken out was measured with LECO oxygen and nitrogen analyzer.Inlaying droplet method was used to analyze the size and distributing characteristics of inclusions,and scan electronic microscope/energy dispersive X-ray microanalysis were used to observe micro-topography and composition of micro-area in inclusion.The results show that with the increase of basicity index,the inclusions in droplet metal become finer and present more uniform distribution,and the composition of inclusion,mainly consisting of Si,Mn and O,is quite different from that of molten slag.The forming mechanism is chiefly based on interfacial chemical reactions of slag-metal and endogenous inclusion combined by bulk diffusion.It is possible to apply inclusions to induce acicular ferrite formation by controlling molten slag basicity index so as to effectively controlling the size of inclusions,and make it become beneficial for weld metal solid transformation.