The application of 1000 MPa grade high-strength steel in the hydropower sector has become increasingly mature, yet there is a paucity of research and development on corresponding high-performance welding materials domestically. Achieving a balance between high strength and toughness in the deposited metal is a critical challenge in the development of such welding materials. Addressing this issue, this paper explores the optimization of deposited metal properties through the addition of rare earth elements to welding materials. Utilizing analytical methods such as OM, SEM, EDS, and XRD, combined with software tools like Matlab, IPP, and CHANNEL5, the study investigates the influence mechanism of rare earth elements addition on the strength, toughness, and inclusions of deposited metal in 1000 MPa grade high-strength steel. The results indicate that the incorporation of rare earth elements enhances the weldability of the welding materials. With the addition of rare earth, the tensile strength of the deposited metal increases from 935 MPa to 960 MPa; however, further addition leads to a decrease in tensile strength, while the yield strength continuously increases by 8.5% to 17.2%. The addition of appropriate amounts of rare earth results in an increase in acicular ferrite and retained austenite content, as well as grain refinement in the deposited metal, leading to an 8.5% to 24.3% increase in impact energy at -40 ℃ and a 15.6% to 42.2% increase at -60 ℃. Additionally, the proper addition of rare earth modifies the inclusions, generating fine, dispersed composite inclusions that bond better with the matrix, thereby optimizing the properties of the deposited metal through various mechanisms. By adding an appropriate amount of rare earth, the properties of the deposited metal in 1000 MPa grade high-strength steel can be significantly enhanced, improving the match between high strength and toughness, and meeting the demands for high-strength steel used in hydropower applications.