The invention relates to a method for preparing a Gamma-Fe2O3 magnetic material by using an abandoned toner cartridge. The method comprises the following steps: taking the abandoned toner cartridge as a raw material, using the characteristic that a black magnetic material Fe3O4 in the abandoned toner generates two variants, namely Alpha-Fe2O3 and Gamma-Fe2O3 when being calcined in air, and preparing the Gamma-Fe2O3 magnetic material by controlling a surface pretreatment process of an organic toner and the subsequent calcination temperature and time. Compared with other preparation methods (such as a coprecipitation method, a chemical vapor deposition method, a non-aqueous media synthesis method, a hydrothermal method, a micro-emulsion method and a high temperature ball milling method) of the Gamma-Fe2O3, the method of the invention has the advantages of being low in preparation cost, simple in process and short in production cycle. The method of the invention takes the abandoned toner cartridge as the raw material, thus the aim of resource utilization of waste materials can be realized, and a simple and fast method is provided for the production and preparation of nanoscale Gamma-Fe2O3 magnetic powders.