The invention discloses a preparation method for a manganese doped cerium dioxide nanoflower visible light photocatalyst and belongs to the technical field of photocatalysts. The preparation method for the manganese doped cerium dioxide nanoflower visible light photocatalyst comprises the specific steps of using a manganese salt and cerium dioxide as raw materials and melted potassium iodide and potassium hydroxide as solvents and heating the raw materials and the solvents at a lower constant temperature of 235-255 DEG C and under a normal pressure for 12-48 hours; cooling the heated raw materials and solvents with a furnace to room temperature; separating out precipitates; washing and drying the precipitates to obtain a manganese doped CeO2 efficient visible light photocatalyst with a flower-shaped structure. The preparation method for the manganese doped cerium dioxide nanoflower visible light photocatalyst, disclosed by the invention, has the advantages that the operation is simple, the needed raw materials are highly available and environmentally friendly, the prepared photocatalytic material has efficient visible light photocatalytic performance, and the organic pollutants can be effectively decomposed.