Abstract: Two different types of weld metals with yield strength of 690 MPa were prepared. The microstructure analysis and mechanical properties test were carried out and the mechanism of strengthen-tougheness was revealed. The results showed that the nickel equivalent ( Ni_eq ) of the traditional 690 MPa grade weld metal was small, and the segregation of alloy elements in the interdendritic region could be negligible. he weld metal formed a relatively uniform structure dominated by coarse granular bainite (GB). Because the coarse GB had little resistance to crack propagation, its low temperature toughness was poor. A new type of 690MPa grade weld metal was prepared by increasing Ni_eq. Due to the significant segregation of Mn and Ni in the inter-dendritic region, the stability of undercooled austenite in the interdendritic region was greater than that in the dendrite region, therefore the weld metal formed a complex phase structure with acicular ferrite (AF) in the dendrite and lath martensite (LM) in the interdendritic region. In this composite structure, AF was the main toughening phase and LM was the main strengthening phase. The yield strength of the weld metal was 738 MPa, and the impact absorption energy at −50 ℃ was 122 J, which achieved a good matching of strength and toughness.