The utility model relates to a site detecting photometer used in water area, in particular to the underwater real-time optic detecting optical fiber probe of portable photometer, consisting of an incident optical fiber, a receiving optical fiber and a consulting optical fiber which can respectively be connected to the optical fiber coupler on the matched existed photometer shell, and a light guiding measuring optical fiber and a light shielding detecting cavity consisting of optical fiber beams combined by optical fiber connectors. The utility model is characterized in rational structure and convenient use; just respectively the utility model at the detecting end of the photometer mainframe optical fiber on the deck of the ship can conveniently and rapidly detect the optic parameter of the water sample in real time.