Sulfonated　Phthalimidomethyl　Zinc　Phthalocyanine　is　a　new　photodynamic　therapy　reagent,　it　can　be　selectively　attacked　to　cell,　but　how　it　attacks　the　target　cell　is　still　unknowable.　The　aggregation　state　of　photosensitizer　is　significant　to　its　mechanism　proved　in　CEL　solution.　The　aggregation　of　ZnPcS2P2　in　CEL　has　been　studied　with　absorption　spectroscopy　and　fluorescence　spectroscopy.　The　aggregation　state　is　dimer　through　theory　analysis,　monomer　molar　absorption　coefficient　as　well　as　equilibrium　constant　were　estimated.