The invention provides an environment-friendly anti-tarnishing red copper bar and a preparation method thereof. The environment-friendly anti-tarnishing red copper bar is obtained by carrying out multi-element intermediate alloy refining and anti-tarnishing modification treatment on raw materials of impure red copper, and the preparation method comprises the following steps: melting electrolytic copper to form molten copper, adding a copper-phosphorus alloy, a copper-lanthanum alloy and a copper-boron alloy into the molten copper and stirring the mixed molten copper until the alloys are molten; allowing the mixed molten copper to stand, carrying out deslagging and casting the mixed molten copper into a mold to form the multi-element intermediate alloy; then smelting and refining the raw materials of the impure red copper after the multi-element intermediate alloy is added into the raw materials, and casting the mixed raw materials into a mold to form and obtain the red copper bar; after polishing, cleaning and wiping the surface of the red copper bar, degreasing and cleaning the red copper bar through ultrasonic oscillation, soaking the red copper bar in the phytic acid/benzotriazole pretreatment liquid, flushing the red copper bar with clear water, then spraying or brushing the anti-tarnishing treatment liquid on the red copper bar, and drying the red copper bar in the cold air to obtain the environment-friendly anti-tarnishing red copper bar.