The invention relates to a fluorescent optical fiber sensor capable of detecting the pH value of blood in real time and a preparation method thereof. A probe of the fluorescent optical fiber sensor comprises an optical fiber and a reception film arranged outside the optical fiber, wherein the reception film contains naphthalene dimethylbenzene anhydride derivative sensitive fluorescent dye linked with the surface of the optical fiber through covalent bonds. The method for forming the probe comprises the following steps in the preparation method: dissolving hydroxyethyl methacrylate or polyethylene glycol diacrylate in deionized water; dissolving the naphthalene dimethylbenzene anhydride derivative sensitive fluorescent dye in the solution; adding catalysts; further adding gamma-methacryloxy propyl trimethoxy silane to obtain the sensitive fluorescent dye solution; and coating the silanized optical fiber with the sensitive fluorescent dye solution to form the probe. The invention has the advantages that the preparation method can effectively prevent the fluorescent carriers from draining and prolong the service life of the fluorescent optical fiber sensor.