As a result of the remarkable advancement of optical fiber technologies, a long-scale ocean measuring system, which has formerly been considered to be impossible to realize, seems to become possible to be developed. A optical fiber measuring system, in which the fiber is used as a sensor element and as a transmission line at the same time, is considered to have the most suitable for ocean measurements, because it enable us to perform the long-scale, continuous and distributed measurements. But the system (sensor) developed so far is only for the distributed temperature measurement in ocean. In ocean, the flow profile measurement is as important as the temperature one. But neither a proposal nor a trial has been presented up to now to apply the system for a long-scale, continuous and distributed ocean flow measurement. In this paper the new concepts of both the flow sensor and the distributed flow sensor using a polarization maintaining optical fiber were introduced. The measuring principle is based on counting the vortex number per unit time (vortex shedding frequency) shedding from one side of a vortex generator using the photoelastic effect generated by the fluctuating lift which acts upon the optical fiber. In order to make clear the usability of the principle, the countability of vortex frequency by the optical fiber must be investigated. Therefore the authors executed preliminary test using city water, and then wind tunnel test to get experimental data in uniform flow. The diameter of the optical fiber used in the tests is 0.9 mm. As a result of the tests, it was clarified that the detection of the vortex shedding frequency of the flow rate was possible in case of the Reynolds number (fiber diameter) greater than 160, and that the flow rate could be calculated by using representative experimental equation derived by Roshko. And the possibility of flow profile measurement was made clear. Thus the authors conclude that this paper gives a basis for development of ocean flow measuring system using a polarization maintaining optical fiber.