The optical window is easy to breed aquatic organisms in the underwater enviroment for a long time. Attached aquatic organisms affect the observation and use of optical windows. In order to restrain or remove the attached aquatic organisms, the method of underwater high speed jet is used. Underwater jet is different from air jet in that it consumes a lot of energy due to the action of environmental water. Because the flow field of the jet in front of the target has a very important influence on the cleaning effect, the underwater jet flow field analysis and experimental study are carried out. In this paper, the flow field parameters before the target are obtained through the analysis of the underwater jet flow field. According to the results of flow field analysis, an underwater jet device is designed. Underwater jet device is composed of submersible motor, pump, nozzle and control box. The test device is used to carry out the underwater jet test, and the flow velocity of 2.2 meters per second at 300 mm before the nozzle is obtained. Using the underwater jet device to regularly carry out the underwater jet to the optical window in the underwater environment can remove the aquatic organisms and dirt attached at the initial stage, and can also inhibit the growth of aquatic organisms, so as to keep the underwater optical window clean.