Abstract The effect of hydrogen on the interfacial reaction between Ti–47Al alloy melt and graphite mold was studied by plasma-arc melting in hydrogen atmosphere. Especially, reduction of recarburization which is harmful to the mechanical properties of TiAl alloys has been investigated. The carbon concentration in the interface of Ti–47Al alloy, as well as the corresponding reaction distance decreases rapidly with increasing hydrogen partial pressure. Activated hydrogen atoms dissociated in high-temperature arc probably take part in the interfacial reactions, represented by [ C ] + 4 [ H ] = CH 4 .