The invention relates to a preparation method for an oxygen-free copper tube for a magnetron. The preparation method is characterized in that the contents of copper and silver in a material of the oxygen-free copper tube is larger than or equal to 99.97%, and oxygen content is smaller than or equal to 0.001%. The preparation method includes following process steps: 1, smelting: placing number 1 high-purity cathode copper in a power frequency induction furnace with a core, raising the temperature of the furnace to smelt the cathode copper into copper liquid, adding lanthanum with the mass fraction ranging from 0.01% to 0.016% into the copper liquid, keeping the copper liquid at the temperature of 1170 +/-10 DEG , and covering a charcoal layer with the thickness ranging from 100mm to 120mm and the charcoal granularity ranging from 40mm to 60mm on the surface of the copper liquid; 2, upward continuous casting; 3, precise cold rolling; 4, recrystallization; 5, cold drawing forming; and 6,finishing. The oxygen content is low, electric conduction is excellent, yield is high, and metal loss is low.