The invention discloses a low-temperature cored tin solder wire and a preparation method thereof, and belongs to the technical field of electronic welding. The low-temperature cored tin solder wire isprepared by adopting a micro-alloying and continuous casting extrusion method, and the low-temperature cored tin solder wire has a diameter of phi 0.3-phi 3.0 mm and a flux solder core of 0.5-4%; andthe low-temperature cored tin solder wire comprises, by weight, 25-55% of Bi, 0.01-2.5% of Ag, 0.01-5% of In, 0.1-5% of Sb, 0.01-1% of Cu, 0-0.15% of Ge, 0-0.15% of Ga, 0-0.15% of P and the balance of Sn. According to the low-temperature cored tin solder wire and the preparation method thereof, multi-element alloy elements of Ag, Sb, P, Ga, Ge and Cu are added and can obviously improve the mechanical property of the solder alloy, the enrichment of Bi can be prevented in the formed welding spots and interfaces by the multi-element alloy elements in a dispersed distribution, the generation of enriched Bi phases are also prevented, and therefore the damage of the hard and crisp enriched Bi phases to the mechanical property of welding joints is reduced and the welding property is improved; the low-temperature cored tin solder wire prepared from the method is carried out the heat preservation and internal stress treatment, and therefore the tensile property of the wire is improved; and thesurface quality and the oxidation resistance of the low-temperature cored tin solder wire are improved through constant-temperature wire drawing treatment.