Preparation method of oxygen-free copper

The invention discloses a preparation method of oxygen-free copper, which comprises the following steps: a copper raw material is subjected to vacuum melting and impurity removal to obtain expected copper liquid, the expected copper liquid is transferred into a refining furnace in a non-vacuum state through a sealed launder, and the refining furnace comprises a heat preservation refining chamber with a first accommodating cavity and a to-be-cast buffer chamber with a second accommodating cavity hermetically communicated with the first accommodating cavity; the expected copper liquid is subjected to refining and impurity removal in the heat preservation refining chamber so that refined copper liquid contained in the first containing cavity can be obtained, and the refined copper liquid flows out of the first containing cavity under the action of first external force, upwards flows and then flows into the second containing cavity; after the first external force is weakened or removed, the refined copper liquid