Fluorescent functionalization of biomass-based materials is of great significance in extending their application scope. In this paper, we summarize the up-to-date research progress of our group in exploitations of fluorescent cellulosic materials by in-situ synthesizing carbon dots (CDs), and their versatile applications in fluorescent sensing and imaging. The cellulose-CDs complexes are advantageous in comparison to other fluorophores in terms of preparation cost, biocompatibility, as well as optical characteristics. However, the construction strategy needs to be optimized for the sake of achieving the complexes with the most desirable properties. Therefore, we proposed a successive esterification-carbonization approach to prepare the cellulose-CDs, which were further applied in the constructions of fluorescent probes for cytoplasm or cell membrane imaging, and fluorescent sensors for heavy/transition metal ions, and biomarker detections.