Through literature review and extensive experiments, it has been found that the method of preparing white ferrous hydroxide flocculent precipitate by reducing oxygen in the device is not only complicated to operate, but also has unsatisfactory experimental results. In this experiment, the author carefully studied the textbook and a large amount of scientific literature, and explored the method of preparing ferrous hydroxide by reducing the amount of dissolved oxygen inside the reaction solution based on practice. Finally, the author"s conclusion is that adding 4-5 drops of 3mol/L or 4mol/L H2SO4 solution to 1-2ml of high concentration (≥ 9mol/L) NaOH solution to prepare FeSO4 solution can produce white ferrous hydroxide flocculent precipitate. The method is simple and highly repetitive, suitable not only for teacher demonstrations but also for student group experiments.