The invention relates to flame-retarded lubricating grease and a preparation method thereof. The preparation method comprises the following technical steps: firstly, putting base oil and an inorganic thickening agent in an open reaction kettle for stirring and mixing, adding a dispersant after heating and heating again to take the mixture out of the kettle for use; secondly, mixing fatty acid calcium soap with the base oil, adding fatty acid lithium soap after heating, keeping heat, dehydrating and refining; finally, removing the materials to a middle kettle, lowering the temperature by cooling, stirring the materials with lubricating grease prepared by the inorganic thickening agent, adding an antioxidant, a flame retardant and an anti-rusting agent for homogenization and filtering to obtain finished products. The lubricating grease not only keeps various excellent properties of original general lithium grease, but also specially enhances the incombustible flame retardance of a 600 DGE C hot plate. Assessment of the properties of the flame-retarded lubricating grease shows that the flame-retarded grease lubricant has excellent mechanical stability, water resistance, lubricating property, anti-rusting property and flame retardance, long service life and low cost, and can replace general lithium grease used in coal mine, subway, metallurgy and other industries at present.