Abstract: Organic dye-sensitized upconversion nanomaterials can expand the absorption of near-infrared light, but dye-aggregation on the surface of nanoparticles limits the improvement of upconversion luminescence. In this paper, sodium 4-(2-((E)-2-((E)-3-((E)-2-(3,3-dimethyl-1-(4-sulfonatobutyl)-1,3-dihydro-2H-benzofindol-2-ylidene)ethylidene)-2-(4-(1,2,2-triphenylvinyl)phenoxy)cyclohex-1-en-1-yl)vinyl)-3,3-dimethyl-3H-benzofindol-1-ium-1-yl)butane-1-sulfonate (CyBTSO) containing tetrastyrene group was synthesized from cyanine IR820 in the presence of strong alkali. IR820 and CyBTSO sensitized upconversion nanocomposites were prepared by a self-assembly method, and their structures and morphologies were characterized. The photophysical properties of dyes in solution and condensed state, as well as the upconversion luminescence of dye-sensitized nanocomposites were investigated. The relationship between molecular structure and upconversion luminescence was systematically studied. It is found that the introduction of tetrastyrene group is not only beneficial to improve the fluorescence quantum yield and lifetime of CyBTSO, but also to enhance its stability and inhibit its aggregation on the nanoparticle surface. Compared with IR820, the stability and the loading amount of CyBTSO on the nanoparticle surface are increased by 1.7 and 3 times, respectively. As a result, a 69-fold enhancement of upconversion luminescence in CyBTSO-sensitized nanocompo-sites excited at 808 nm is achieved compared to that in β-NaYF₄:Yb20%, Er2% excited at 980 nm. This work provides a theoretical reference for the development of upconversion materials with high upconversion efficiency and stability.