Abstract: The harsh deep-sea environment requires welded structural components to possess an excellent strength-plasticity match. However, limited dislocation slip behavior under high stacking fault energy leads to poor plastic deformation capacity in titanium alloy weld metal. Based on first-principles calculation, the effects of substitutional doping elements on the stacking fault energy and surface energy of titanium alloy weld metal were first studied; then, the composition design of titanium alloy welding materials for deep-sea equipment was conducted, and finally, the performance validation of the all-weld metal was completed. The results indicate that all nine substitutional doping elements decrease the stacking fault energy and increase the surface energy, which helps to improve the plastic deformation capacity by promoting dislocation slip and suppressing crack formation. Among them, Cu and Fe have the most significant effects. Based on the evaluation of plasticity, the effects of substitutional doping elements on the strength and microstructure were also comprehensively considered, and then a novel titanium alloy welding material with a composition of Ti−4Cu was designed. The microstructure of Ti−4Cu is composed of fine equiaxed prior-β grains, with an ultimate tensile strength of 1 049 MPa and an elongation to fracture of 14.8%, exhibiting an excellent strength-plasticity match.