The invention discloses a graphene doped ammonium polyphosphate flame retardant coated fabric and a preparation method thereof. A base material of the fabric is provided with a hydrophilic surface, and a surface of the fabric is coated with a flame retardant coating; the flame retardant coating is an ammonium polyphosphate material coated with graphene oxide sol. According to the graphene doped ammonium polyphosphate flame retardant coated fabric, the effects of graphene and ammonium polyphosphate can be synergetically achieved, thus endowing the fabric with excellent flame retardance; the preparation method has the advantages of simple process, environment friendliness, no toxicity, water saving and suitability for large-batch industrialized production.