The invention discloses a precious metal nano-particle preparation method based on modified collagen. The method includes dissolving the modified collagen in deionized water, heating and stirring; adjusting potential of hydrogen (pH) value of a collagen solution by a hydrochloric acid and a sodium hydroxide solution, adding a precious metal precursor, reacting at the temperature of 60 DEG C to 100 DEG C to obtain monometallic nano-particle, adding another precious metal precursor, and continuously reacting at the temperature of 60 DEG C to 100 DEG C to obtain a double precious metallic colloid. By means of the method, the size of the nano-particles is regulated by changing the pH of the modified collagen solution, and the novel study filed of the nano-particle preparation method is developed; a plurality of amino acid sequences in the collagen have intensive binding effect on Au and Ag nano-particles, the precious metal nano-particle colloid is salt-resistant and high in pH stability, and the novel filed of the application of collagen in the biological materials is developed.