The present disclosure discloses preparation and application of a novel multifunctional nanocomposite material with new photosensitizer, and belongs to the technical field of photodynamic therapy and the field of biomedicine. The photosensitizer multifunctional nanocomposite material provided by the present disclosure is prepared by self-assembly of cercosporin and an acid-sensitive copolymer multifunctional material with liver tumor cell targeting ability and traceability, wherein the acid-sensitive copolymer multifunctional material can be a copolymer of poly(N,N-dimethylaminoethyl methacrylate) and poly-3-azido-2-hydroxypropyl methacrylate covalently linked by galactose-modified rhodamine B. The photosensitizer multifunctional nanocomposite material disclosed by the present disclosure can specifically recognize liver tumor cells and be endocytosed into the cells through galactose-asialoglycoprotein receptor interaction, and can trigger the release of the photosensitizer cercosporin under acidic pH conditions to exert photodynamic therapy efficiency. The novel photosensitizer multifunctional nanocomposite material has a good application prospect in targeted photodynamic therapy of tumor cells.