The invention discloses a preparation method for a nanometer metal/red phosphorus photoelectric composite material. The preparation method comprises the following step that firstly, nanometer red phosphorus is placed in water for ultrasound treatment to obtain a nanometer red phosphorus dispersion solution, and a metal precursor aqueous solution is prepared; then the nanometer red phosphorus dispersion solution and the metal precursor aqueous solution are mutually added by drops, and then in-situ reduction compound is conducted after even stirring; and finally the product is filtered, washed with water and dried to obtain the nanometer metal/red phosphorus composite material. According to the preparation method for the nanometer metal/red phosphorus photoelectric composite material, a reducing agent, a protective agent and a dispersing agent are not added while preparing nanometer metal particles, and the preparation method is green and simple; and the product has good stability, largespecific surface area, distribution and the sizes of metal particles are uniform, and the composite has good photoelectric response characteristic.