The invention discloses a method for degrading organic waste water by photo-assisted activation of potassium hydrogen persulfate through bismuth ferrite, belonging to the technical field of waste water treatment. A perovskite structure BiFeO3 in the invention has a spherical morphology and is prepared by adding a certain amount of a surface active agent under hydrothermal conditions; the specific surface area is high; and the prepared BiFeO3 self can degrade organic pollutants by photocatalysis under the irradiation of visible light. According to the method disclosed by the invention, BiFeO3 is applied to degrading the organic pollutants by activating potassium hydrogen persulfate; the methyl orange degradation rate within 15 min is 94%; the methyl blue degradation rate within 40 min is 90%; the rhodamine degradation rate within 40 min is 65%; by means of combined use of BiFeO3 and potassium hydrogen persulfate, the organic pollutants are oxidized and degraded; the organic pollutants can be effectively degraded under better illumination conditions; the organic pollutants can also be effectively oxidized and degraded without light or under poor illumination conditions; and therefore, the method has good application prospect.