Provided are a visible-light catalyst Bi3O4Br and a preparation method thereof. The method comprises adding deionized water, 
bismuth salt and 
quaternary ammonium salt into a reaction kettle to obtain the 
bismuth salt with concentration of 0.02-0.04 
molar / 
liter and the 
quaternary ammonium salt with concentration of 0.02-0.05 
molar / 
liter, wherein the 
molar ratio of the 
bismuth salt to the 
quaternary ammonium salt is larger than or equal to one; adding caustic soda solution with concentration of 1 molar / 
liter into the mixture with stirring to regulate potential of 
hydrogen (pH) to be 11.0-12.5; stirring and performing hydro-
thermal treatment at the treatment temperature of 160-180 DEG C; after keeping the constant temperate for 12-18 hours, centrifugally separating 
solid products; respectively washing the obtained 
solid products through the deionized water and absolute ethyl 
alcohol for at least three times; and 
drying the products at the temperature of 50 DEG C for at least 6 hours to obtain light-yellow Bi3O4Br 
solid powder. The Bi3O4Br has good visible-
light activity and can have strong degradation to various pollutants under the 
irradiation of the visible light. In addition, the method is simple in synthesis, the whole synthesis process is easy to control, raw materials are easily obtained, and the cost is low.