The invention discloses a method for preparing nanoparticles, and in particular relates to a method for preparing gold nanoparticles (AuNPs). The method comprises the following steps: firstly preparing intrinsic silicon wafers of a certain size and an SDS (sodium dodecyl sulfate) solution with certain concentration by adopting a pure physical method; spin-coating SDS on the intrinsic silicon wafers by a spin-coating method; plating an Au-film layer on the SDS-coated silicon wafers by a magnetron sputtering method; carrying out ultrasonic treatment to obtain nanoparticles; and finally carrying out centrifugal separation to obtain the AuNPs. Compared with the traditional process, the method is cleaner, more convenient, faster and more environmentally-friendly.