A water mixing amount stabilizing device for an oil well comprises a shell (1), a filter net (2), a baffle (3), a water nozzle (4) and sealing rings (5). The water mixing amount stabilizing device is characterized by being of a cylinder shape; the shell (1) is provided with a stepped central hole; the large hole segment of the central hole is provided with internal threads; the sealing rings (5) and the water nozzle (4) are sequentially installed in the large hole segment; the baffle (3) is connected with the internal threads of the large hole segment to compress the water nozzle (4); the filter net (2) is installed outside the internal threads of the large hole segment. According to the characteristic of stabilizing the water amount, based on the set requirements of the oil well for the water mixing amount, and the water mixing amount remains to be a fixed value by adjusting the nozzle; when the water mixing amount stabilizing device is used, after water mixing coefficients are calibrated at a time, the water mixing amount can be stabilized and free of adjustment without adjustment and further maintenance; in this way, the problem that metering of crude oil in a water mixing well is inaccurate due to water mixing fluctuation is avoided, the labor difficulty of workers is lowered, and a basis is provided for management measure development of oil wells.