The invention discloses a method for preparing a copper-based solder. The method comprises the following steps: (1) burdening: preparing a furnace burden from copper, manganese, nickel, cobalt, silicon, a copper-ferrous intermediate alloy, a copper-boron intermediate alloy and a copper-mixed rare earth intermediate alloy serving as raw materials; (2) casting: putting the prepared furnace burden into the a corundum crucible according to the sequence of manganese, copper, nickel, cobalt, silicon, copper-boron intermediate alloy, copper-mixed rare earth intermediate alloy and copper-ferrous intermediate alloy, smelting by adopting medium-frequency induction, and cooling along with the furnace to obtain an alloy blank, wherein the smelting process is performed under the protection of argon gas; and (3) rolling: rolling the alloy blank with a cold-rolling mill to obtain the copper-based solder. The copper-based solder provided by the invention can be applied to an ODS (Oxide Dispersion Strengthened) high-temperature alloy welding joint, has high brazing process performance, heat resistance, corrosion resistance and machining process, and is low in cost.