The chemical composition formula of the zinc-germanium oxide long-afterglow luminescent material is Zn2GeO4: XC, C is Eu < 3 + > or Dy < 3 + >, and X is greater than or equal to 0.001 and less than or equal to 0.1. The preparation method of the oxide comprises the following steps: taking a proper amount of raw materials to prepare a solution with a certain concentration, mixing in a beaker according to a certain proportion, adjusting to a required pH value, magnetically stirring uniformly, loading into a high-temperature reaction kettle with a polytetrafluoroethylene lining, heating to 220 DEG C, keeping the temperature for 4 hours, and cooling to room temperature after the reaction is finished, taking out a reaction product, centrifuging, washing and drying to obtain a product. The material obtained by the invention can emit green afterglow after being irradiated by ultraviolet light, the afterglow time can reach 500 seconds, and the long afterglow material takes Zn, Ge and O elements as a matrix and Dy < 3 + > or Eu < 2 + > as an afterglow luminescence center, and has better thermal stability and chemical stability. The innovation of the invention is that a rare earth material is introduced as an activator, the long-afterglow luminescent material is synthesized by a hydrothermal synthesis method, the synthesized long-afterglow luminescent material has small and relatively uniform particle size and excellent sustainable luminescence performance, and provides possibility for in-depth study of in-vivo imaging, biological targeted therapy and other medical fields.