The invention discloses a DOPO-based expanding fire retardant. The DOPO-based expanding fire retardant comprises, by mass, 50-60% of graphene containing a DOPO group, 30-40% of melamine salt of starch phosphate, 5-10% of tea saponin and 5-10% of a dispersant. The formula of the DOPO-based expanded fire retardant is reasonable, the main body fire retardant is graphene containing the DOPO group, the DOPO group has excellent fire retardation property, and the addition of graphene is beneficial to improve and maintain the mechanical strength of a formed film; and the melamine salt of starch phosphate in the formula is an expanding fire retardant, is usually prepared from starch, polyphosphoric acid and melamine, and has the advantages of wide sources of raw materials, low cost and less toxicity, the melamine salt of starch phosphate and the graphene containing a DOPO group form a main body system and have fire retardation synergism, so the DOPO-based expanding fire retardant is easy for being widely promoted and applied.