The invention belongs to the technical field of luminescent materials, and discloses a red germanate long-afterglow luminescent material and a preparation method thereof. The method comprises the steps: according to the stoichiometric ratio of the chemical composition of Mg[2-y-z]Ge[1-x]O[4]:xMn<4+>,yYb<3+>,zLn<3+>, (x=0.001-0.20, y=0.005-0.10, and z=0-0.10), weighing MgO, GeO2, MnO2, Yb2O3 and Ln2O3, grinding uniformly, then in an oxidizing or inert atmosphere, sintering at high temperature, and cooling to obtain the red germanate long-afterglow luminescent material. The long-afterglow luminescent material does not contain sulfur, and has the advantages of good physical and chemical stability, cheap and easily obtained raw materials, and low cost; at the same time, compared with an Eu<2+> activated broadband-emission red long-afterglow luminescent material, the long-afterglow luminescent material provided by the invention has purer luminescent color, and has the emitted light closer to standard red light.