The invention provides a production method and process of a copper or copper alloy cast ingot with a diameter of 800mm, which is characterized in that two or more induction furnaces are used together in a smelting process for producing a cast ingot; copper or copper alloy with the same alloy brand is simultaneously smelted in two or more induction furnaces, after the copper or copper alloy in each induction furnace is respectively smelted, the cast ingot is cast on one of the induction furnaces, and the copper or copper alloy solution in each of the other induction furnaces is in a heat insulating state; and after a part of the copper or copper alloy solution in the induction furnace to be used for casting the cast ingot is used, a copper water drum and an overhead traveling crane are used for respectively transferring the copper or copper alloy solution in each of the other induction furnaces into the induction furnace for casting the cast ingot. The casting process conditions are asfollows: the casting temperature is 1180 DEG C, and the upper and low temperature difference can not exceed 5 DEG C; the speed of cooling water is controlled at 13 cubic meters/hour, and the water inlet temperature is controlled at 20 DEG C; the casting speed is controlled at 1.2-1.4 meters/hour, and the casting speed needs to be constant; and the coal gas protection needs to be sufficient.