The present invention provides a method for preparing an injectable thermosensitive chitosan/TEMPO-oxidized cellulose nanofibers hydrogel. The injectable thermosensitive chitosan/TEMPO-oxidized cellulose nanofibers hydrogel exhibits superior biocompatibility through addition of TEMPO-oxidized cellulose nanofibers, and excellent cell proliferation and bone regeneration through cellular interaction, and is gelled in vivo, thus being highly useful as a filler for wound healing and bone regeneration. In addition, the injectable thermosensitive chitosan/TEMPO-oxidized cellulose nanofibers hydrogel exhibits excellent porosity, has an interconnected structure and is thermogelling, based on thermosensitivity of undergoing a sol-gel transition depending on temperature, thus inducing rapid gelation in vivo and facilitating bone regeneration upon implantation in vivo.