Black brick for repairing ancient building wall and preparation method thereof

The invention discloses a black brick for repairing ancient building walls, the black brick comprises a green brick, inner fibers and an outer coating, the inner fibers are arranged in the green brick, the outer coating is arranged on the outer wall of the green brick, the green brick comprises the following raw materials by weight: 14-18% of Portland cement, 66-74% of ceramsite, 2-4% of a concrete coloring agent, 2-5% of zeolite and the balance of water; and the inner fiber is glass fiber. The bonding capacity between the ceramsite and the cement mortar is high, so that the black brick has high impermeability and durability, when the interior of the black brick is corroded by rainwater and pulverized, gas can be generated, the zeolite can effectively absorb the gas and prevent the gas from expanding the black brick, and the crossed glass fibers in each layer improve the stress resistance of the black brick, so that the service life of the black brick is prolonged. And under the support of the glass fibers, t