The chiral liquid crystal self-assembly behavior of cellulose nanocrystals (CNC) opens a fantastic way to design functional nanocomposites with advanced optical properties. Herein, we demonstrate that crack free, large size thermal reduced graphene (TRG)/CNC composite films with highly ordered, layered structures at the submicrometer level can be obtained through a vacuum-assisted self-assembly (VASA) technique. The results show that the addition of a small amount of TRG (≤0.5 wt%) is compatible with the self-assembly of CNC under flow field. Benefiting from the homogeneous dispersion of TRG in the chiral nematic phase of CNC, the resultant TRG/CNC films present uniformly metallic iridescence, which can be reversibly changed by the hydration or dehydration process similar to the water response of beetles Tmesisternus isabellae's elytra. Moreover, the TRG/CNC composite film with only 0.3 wt% TRG loading exhibits high electrical conductivities. This study demonstrates that it is feasible to combine the intriguing self-assembly ability of CNC with the extraordinary optical and electrical properties of graphene for constructing multifunctional biomimetic materials and sensors.