The invention relates to a release agent for molten iron casting. The release agent comprises the following raw materials by weight: 40-50% of quicklime, 20-30% of yellow mud powder and 20-40% of coal powder which are matched. The specification of the quicklime and the yellow mud powder is that 180-200 mesh quicklime and yellow mud powder occupy over 80% of the total, and the coal powder with granularity lower than 5mm occupies over 90% of the total. The release agent has the advantages of being high in adhesion capability on an iron cast mould and even in coating; enabling iron block demoulding rate to reach over 98%; facilitating observation in matching of the release agent and being capable of well controlling viscosity; greatly improving abrasion resistance and scraping resistance; being low in unit price due to the fact that the quicklime and the yellow mud powder are less in quantity; and saving resources and reducing production cost due to the fact that the releasing agent flushed by cooling water from the iron casting mould precipitates in a circulation gutter and a precipitation tank and can be recycled to serve as a part of raw materials to rematch the release agent after impurities are removed simply.