The invention discloses a method for determining mass of metal particles with specific particle content. A calculation method is used for relatively accurately estimating the mass of the metal particles with the specific particle content according to particle size distribution information of the metal particles by means of particle size distribution information of particles so as to obtain metal particle impurities with specific particle quantity through a weighing manner. The method lays the foundation for researching the influence of metal particle quantity on oil breakdown voltage of a transformer.