A coating liquid for preparing a needle-shaped cylinder liner, comprising the following components: 0.05-0.4 parts of an anionic surfactant; 0.05-0.5 parts of tannic acid; 0.15-0.7 parts of caustic soda; 22-38 parts of diatomite; 3-10 parts of montmorillonite; and 62-75 parts of water. A method for preparing a needle-shaped cylinder liner comprises spraying a coating liquid for preparing the needle-shaped cylinder liner onto the inner wall of a hollow cylindrical mould, and drying the coating liquid to obtain a mould with a coating attached to the surface of the inner wall; adding an inoculated iron liquid into the rotary mould, and cooling and demoulding to obtain a cylinder liner blank; and subjecting the blank to outer surface cleaning and forming machining to obtain the needle-shaped cylinder liner.