The invention relates to a ceramsite sand for casting and a preparation method thereof. The ceramsite sand comprises the following chemical components in parts by weight: 35-65 parts of silicon dioxide, 30-50 parts of aluminum oxide, 1-10 parts of iron oxide, 1-4 parts of manganese dioxide and 2-8 parts of chromic oxide. The method comprises the following steps: performing grinding, and detecting the chemical composition and contents of the raw materials; and sequentially performing proportioning, ball making, screening, sintering and grading to obtain the finished product. The ceramsite sand prepared by the invention is high in thermal conductivity and refractoriness, conforms to the requirements for casting sand, can be used for casting and casting mold production instead of silica sand, chromite sand and the like, reduces the discharge amount of solid waste in the casting industry, and improves the quality of cast products.