PDA nanosheets were prepared by in-situ coating magnesium hydroxide nanosheets with hydrophobic cotton cloth as the substrate, polydopamine (PDA) as the raw material and magnesium hydroxide as the template, and then PDA nanosheets composite filter membrane (referred to as composite filter membrane) was prepared with hydrophobic cotton cloth as the substrate. The structure of the composite filter membrane was characterized by SEM, TEM, BET, FTIR, XPS, XRD and contact angle tester. The separation performance, recycling performance and anti-pollution performance of the composite filter membrane for oil-water mixture and emulsified oil were measured. The results showed that the introduction of PDA nanosheets significantly increased the surface roughness of the composite membrane. Under the condition of self-weight, the permeation fluxes of the composite membrane for oil-water mixture and emulsified oil were 2866.24 and 1015.13 L/(m2?h), respectively, and the separation efficiency was 99.1%. The permeation flux of the composite membrane for emulsified oil was 789.11 L/(m2?h) and the separation efficiency was 98.1% after repeated use for 10 times. In addition, PDA nanosheets also have universality and can cover different substrates for emulsified oil separation, which has good application prospects.