The invention relates to the technical field of welding wire preparation, and specifically discloses a preparation method of tin-bismuth alloy welding wire. In the continuous rolling step, the tin-bismuth alloy is hot-rolled at a specific deformation rate and deformation temperature. , bismuth atoms can be solid-dissolved in the lattice of tin to a large extent, reduce the equivalent of bismuth phase, and improve the plasticity of the alloy; under the specific conditions of the present invention, the deformability of tin is significantly increased, the yield strength is reduced, and the softening ability is greatly improved Reinforced, it can rapidly deform under external stress, resolve the stress impact, and prevent the matrix from cracking. As the deformation progresses, although the bismuth phase breaks during "rolling" and mutual friction, it will produce fine lines, but the deformation is slower. At high speed, the fine lines will be quickly filled with tin, and the alloy shows good plasticity macroscopically, which provides favorable conditions for subsequent continuous wire drawing.