The invention discloses a preparation method of a lead-tin-based solder alloy. The preparation method comprises the following steps that (1), powder preparing is carried out, specifically, the following raw material of, in percentage by weight, 45-60% of Sn powder, 25-35% of Pb powder, 10-25% of In powder, 1.5-5% of Bi powder, 0.02-0.08% of Tb powder, 0.1-0.7% of Zr powder, 0.7% of Fe powder and the balance of Se powder are mixed; and (2), sintering is carried out, specifically, the mixed powder is put into a graphite mold, pre-pressing is carried out, the pre-pressed mold is put into a sparkplasma sintering furnace, vacuumizing is carried out, the sintering pressure is 50 Mpa, the heating rate is 45 DEG C/min, the temperature is raised to 520 DEG C, then heat preservation is carried outfor 5 min, and after furnace cooling, lead-tin-based solder alloy is prepared. The invention further provides the solder alloy prepared by the preparation method. The lead-tin-based solder alloy has the beneficial effects that the microstructure of the lead-tin-based solder alloy is uniform and compact, the wettability of the solder alloy is improved, and the lead-tin-based solder alloy has a lowmelting point.