A sensing device with a sealing structure for measuring fluid characteristics by a photoelectric method is disclosed. The sensing device includes an electrode head having an outer side which contacts a fluid to be measured and one or more windows arranged in respective window openings which extend between an inner and an outer face of a wall of the electrode head. At least two sealing structures seal the one or more windows and the respective window openings. A first of the at least two sealing structures is bonded, welded, or provides an interference fit. The sensing device can be used to seal the product in high temperature, high pressure, and corrosive environment, so that the product has high air tightness and is stable and reliable for a long time. In addition, the sealing structure of the product is easy to clean.