In this contribution, a green nanocomposite consisting of casein phosphopeptide-biofunctionalized graphene oxide nanoplatelets (CPGO) and cellulose nanofibers (CNFs) was fabricated via vacuum-assisted self-assembly technique. A ‘natural nacre’ and strong hydrogen bonds network structure was constructed by CNFs and CPGO. In this architecture, the scaffold of one-dimensional CNFs is employed as the structural component to construct hydrogen bonds network and reinforce mechanical strength, while the arranged two-dimensional CPGO in the framework provides a convenient pathway for in-plane acoustic phonon transmission. The as-obtained nanocomposite possesses high in-plane thermal conductivity of 12.75?W?m^?1 K^?1 and favourable tensile strength of 33.45?MPa. The theoretical simulation results indicated it has low thermal resistance between CPGO. Furthermore, a phosphorus-nitrogen flame retardant system was built and fire experiments presented that it could effectively prevent flame spreading. Heat release rate curve results showed that the total heat release and peak heat release rate decreased by 58.6 % and 20 % than CNFs, respectively. Cooling down experiments for LED chips showed that nanocomposites have an excellent cooling rate (8.85?°C?min^?1) which can transfer efficiently heat energy and demonstrated its potential usefulness in electronic device-cooling applications.