Abstract: Super-hydrophilic-underwater super-oleophobic materials, also known as ‘water removal’ materials, have the characteristics of filtering water and absorbing water but not oil. Inspired by the super-hydrophilic nature of the surface of fish scales such as hydroxyapatite and thin mucus, it uses discarded oyster shells as raw materials, and uses nano-hydroxyapatite and original PU sponge as the building blocks. The HAP/PDA type oyster shell coating was successfully constructed on the surface of the PU sponge through a simple solution dipping process, and the super-hydrophilic-underwater super-oleophobic HAP/PDA super-hydrophilic/underwater super-oleophobic sponge was obtained. The addition of HAP can regulate the growth of HAP particles into a papillary structure, increase the surface roughness of the sponge, and thereby improve the surface wettability and oil-water separation performance of the sponge. A variety of oil-water mixtures can be separated only under the action of gravity, and the separation efficiency of various oil-water mixtures can reach more than 95%. It is easy to clean and has good reusability and mechanical stability. After 10 cycles of use the separation efficiency has not been significantly reduced. Used in combination with a pump, it can be used in the separation process of a large amount of oily wastewater.