The invention discloses a melting and casting equipment provided with a single furnace and an integrated crucible and used for producing high-cleanliness magnesium or magnesium alloy and a process for producing the high-cleanliness magnesium or magnesium alloy and belongs to the technical field of metal smelting. The device is composed of the heating furnace and the integrated crucible which is divided into three chambers by division plates. The chambers are a melting chamber, a purification chamber and a heat insulation standing chamber according to functions. The chambers communicate with each other through openings. The effect of the melting chamber is to melt magnesium or magnesium alloy or lead in liquid state melt of the magnesium or the magnesium alloy; the purification chamber enables the melt to pass through a screen cloth I and a screen cloth II which are soaked in a molten liquid flux to make the melt come into full contact with the flux, and thus the goal of removing impurities in the melt is achieved. The purified melt floats and is gathered and then enters the heat insulation standing chamber to undergo follow-up pouring operation. According to the melting and casting equipment and the process, the magnesium or the magnesium alloy is purified thoroughly, operation workers' operation difficulty is reduced, continuous production can be performed, the production efficiency is high, and the environmental pollution of the process is lower than that of a conventional process.