The cellulose is the most abundant natural based polymer materials, has the advantages of renewable and biodegradable. The extraction process of cellulose into nanocellulose via up-bottom design strategy could afford high-performance to the materials. Cellulose nanofibrils (CNFs) are flexible, high-strength fibrils disintegrated from chemical wood pulp fibers, with typical diameters in the 3-10 nm range and lengths in the 0.7-2 μm range. To produce high performance CNFs-based functional materials, our recent studies combined CNFs and 2D nanoclays to construct nacre mimicking multifunctional nanocomposite films via 1D/2D assembly method. The charge density and geometry of the CNF and 2D platelets are tuned, and the aggregation and porous structures are controlled to increase the mechanical properties, and optimize the thermal-shielding and fire-retardancy properties. The complex hierarchical structures of the nacre-mimicking films were investigated by synchrotron X-ray scattering (WAXS and SAXS), with in-situ investigations of nanostructural changes of CNF and 2D clay platelets during drying were performed. Changes in the out-of-plane orientation of CNF were determined. Residual drying strains previously predicted from theory were confirmed in cellulose due to capillary forces. The formation of CNF aggregations could be followed. These investigations provide facile strategy to construct bio-inspired high-performance CNFs-films, and illustrate the nanostructural changes during 1D/2D assembly.