Magnesia-calcium materials have stable hot performance, good resistance to the erosion and corrosion of liquid steel and steel slag, and a special role in purifying liquid steel, so they are widely used in iron and steel industry. However, hydration of magnesia-calcium materials seriously restricts their use, so researches have been done to improve their hydration resistance, obtaining a series of achievements. In this paper, the improvements on the hydration resistance of magnesia-calcium materials by additives in recent 20 years were presented, and their mechanisms were summarized.