Developing an antifouling and stable separation poly (vinylidene fluoride) (PVDF) membrane for water treatment is of great significance but challenging due to the limitations of its low surface properties and strong hydrophobicity. In this study, a novel multi-block composite ultrafiltration membrane was developed using the mosaic-assembled doping of pineapple leaf nanocrystalline cellulose and g-C3N4. The effects of adding different components on the PVDF composite membrane properties have been analyzed. The surface chemical composition, surface morphology, crystallinity and thermal stability of the composite membranes were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Both of the tensile strength and elongation length of the PVDF composite membranes were enhanced due to the addition of pineapple leaf nanocellulose and g-C3N4, and the tensile strength and elongation length of PVDF/PEG/g-C3N4/Pineapple leaf nanocellulose composite membrane can reach 10.61 MPa and 8.85 mm. The porosity of the PVDF composite membranes was 46.6%, respectively. The water flux and flux recovery ratio of PVDF/PEG/g-C3N4/Pineapple leaf nanocellulose also can reach 256.75 L/(m2 ⋅h) and up to 82.1%. All the above experimental data showed that the addition of pineapple leaf nanocellulose and g-C3N4 can greatly improve the performance of the PVDF composite membrane. The prepared modified membrane has potential application value in the field of wastewater separation and treatment.