Abstract: In this paper, the MAG welding using 80%Ar+20％CO₂ was applied on a Ti-Nb type microalloy TMCP high-strength steel. The mechanical properties of the welded joint before and after drawing temper treatment were particularly investigated, which aimed at clarifying the softening mechanism of welded joint systematically and comprehensively analyzing the correlation between the variation of mechanical properties and microstructure. The results showed that with increasing of heat input, the precipitated particles of (Ti.Nb)(C,N) were dissolved during the welding thermal cycle, which improved the softening tendency of CGHAZ. The post drawing temper treatment mitigated the softening behaviors of welded joints and the strength of the base metal were improved. Moreover, with the increase of tempering temperature, the impact toughness of welded joint and base metal were decreased, due to the inheritance of original microstructure and the precipitation of Fe₃C-typed carbide along grain boundaries.