The invention relates to a functional additive for improving the crack self-repairing performance of a cement-based material as well as a preparation method and a use method of the functional additive, and belongs to the technical field of building materials. The functional additive comprises the following components in parts by weight: 30-100 parts of cement and 20-70 parts of a magnesium oxide expanding agent. The water-cement ratio of the functional additive is 10-20%. The functional additive can effectively improve the crack self-repairing performance of the cement-based material, so thatthe durability of the cement-based material is improved. The preparation method is simple and easy to operate, cheap and easily available in raw materials and suitable for expanded production.