Abstract: The influence of oxygen content in shielding gas during MAG welding on the type, size, quantity, and distribution of oxide inclusion and the content of residual austenite, reversed austenite and impact toughness of 00Crl3Ni5Mo deposited metal was investigated. It was found that Si-Mn-O, Si-Mn-Al-0 composite oxide inclusions were the main reason for the degradation of impact toughness of 00Crl3Ni5Mo deposited metal. The oxide inclusions in 00Cr13Ni5Mo deposited metal could inhibit the generation of reversed austenite during tempering. With the increase of oxide inclusions, the content of reversed austenite decreased.