Directed at the phenomenon that improper disposal in storage and transportation of powdered rubber easily causes spontaneous combustion, the invention provides a preparation method for flame-retardant powdered rubber. According to the method, carbon tetrachloride and the like are used as halogen donors, unsaturated fatty acid anhydride and the like are used as halogen acceptors, and the halogen donors and the halogen acceptors are subjected to an addition reaction and to saponification by an aqueous sodium hydroxide solution so as to prepare an isolating agent with a flame retardation function; then, the isolating agent is used for preparation of powdered rubber to produce a powdered rubber product with flame resistance; safety of the product in the processes of storage and transportation can be guaranteed.