Elementary particles can be classified according to their spin quantum numbers and electric charges. As the three features of elementary particles are spin, electric charge and mass, they could also be classified according to their masses. Our work hypothesized a model for the masses of elementary particles, in which a formula for the mass of an elementary particle in a set of modified atomic units (called Hartree-Chen atomic units) consists of a Time Factor (TF) times a Space Factor (SF) along with at least one Sub-space Factor (SSF) in the format of mP/au=[TF(SF±Σ1/SSF)]2, -2. It seems that elementary particles should have two genders, i.e., Yang and Yin according to the ± symbols before 1/SSF-1st, and the Yang/Yin ratio of all quarks and leptons is 1/2. With the model, all masses of elementary particles (including neutrinos and the particle of dark matter) in Hartree-Chen atomic units were calculated, the mystery of three generations of quarks and leptons could be explained, the matter-antimatter asymmetry problem of the universe could be solved, and the composition of the universe could be interpreted. In the end, a picture and a table of mass model of elementary particles are presented.