The utility model discloses a device for measuring water in oil and water separation. The device comprises at least two successively-arranged measuring cylinders, wherein the upper end of each measuring cylinder is open, and the lower end of the measuring cylinder is provided with a base; a flow guide branch pipe is arranged between two adjacent measuring cylinders; an entrance end of the flow guide branch pipe is communicated with the upper part the previous measuring cylinder, and an exit end of the flow guide branch pipe extends to the opening at the upper end of the adjacent following measuring cylinder; the flow guide branch pipe is connected on the measuring cylinder in an uptilting manner; and the height of the highest point of the flow guide branch pipe is lower than that of the opening at the upper end of the measuring cylinder connected with the flow guide branch pipe. By the scheme disclosed by the utility model, the separation is performed by using the principle of oil and water density difference, and through the side-by-side arrangement of the plurality of unidirectionally-communicated measuring cylinders, the oil and water separation can be sufficiently conducted on an oil-water mixture generated in an indoor oil displacement experiment; and the device has the advantages of high measurement accuracy, simple structure, low cost, convenience for cleaning, and the like. The device is adapted to performing the oil and water separation on the oil-water mixture generated in the indoor oil displacement experiment in a tertiary oil recovery room.