An optimization method is used to obtain the longest effective afterglow time in the rare earth ions doped long lasting phosphors. The effective afterglow time is defined as the time for the intensity to decays to 10% of the initial intensity. In this paper, we choose the Eu²⁺ and Dy³⁺ coped Sr₂MgSi₂O₇ as the experimental objects. In order to obtain the longest effective afterglow time of Sr₂MgSi₂O₇:Eu²⁺, Dy³⁺ phosphor, the experiment is optimized by quadratic general rotation combination design. The Sr₂MgSi₂O₇:Eu²⁺, Dy³⁺ phosphor are synthesized via a solid-state reaction. The effective afterglow time is obtained by the afterglow decay curve. A binary quadratic regression equation model relating the rare earth ions Eu²⁺/Dy³⁺ doping concentrations to the effective afterglow time is established. The genetic algorithm is used to solve the equation. The optimal doping concentration of Eu²⁺ and Dy³⁺ are 0.5 mol% and 1.0 mol%, respectively. The theoretical maximum value of effective afterglow time is calculated to be 321 s. The phosphor with the optimal doping concentration Sr₂MgSi₂O₇:0.5 mol% Eu²⁺, 1.0 mol% Dy³⁺ are synthesized by the same method as that of synthesizing the frontal samples. The X-ray diffraction shows that the optimal sample prepared is of pure phase, and the doping ions have no effect on the lattice structure of the matrix. A characteristic emission at 465 nm due to the 4f⁶5d¹−4f⁷ transition of Eu²⁺is observed under the 370 nm excitation. The afterglow curve of the optimal sample is measured and the effective afterglow time is 333 s which has a good match with the theoretically calculated value of 321 s. The thermoluminescence spectrum of the optimal phosphor is measured, and the trap depth is calculated to be 0.688 eV according to the Chen’s model. Moreover, the long-lasting luminescence process of Eu²⁺ as the luminescence center of Sr₂MgSi₂O₇ matrix is discussed in the energy level diagram.