Disclosed are a cyanine dye compound and a preparation method therefor, and adual-function agent for photodynamic therapy and a preparation methodtherefor. Theprovided cyanine dye compound is connected to multiple markers, which improvestheaccuracy of combination of dye and tumor cells, effectively reduces thebackground value,and avoids excessive residues in the liver. The provided cyanine dye compoundis conjugatedwith the photosensitizer at 2'" position, so that tumor highly absorbs theconjugates.