Magnesium hydroxide (MH) and an intumescent flame retardant (IFR) have been incorporated into a thermoplastic vulcanizate (TPV) for the purpose to fabricate halogen-free flame retardant elastomeric materials. Significant synergistic effects of MH and IFR have been observed for the TPV in terms of both flame retardant properties and mechanical performance. The mechanism of the synergistic effects has been investigated. The results indicate that a small amount of IFR accelerates the degradation of the matrix and induces a shrinkage matrix, leading to a compact and unbroken MgO protective layer. Such compact MgO layer on the surface of the material prevents the bulk material from further degradation, and a high flame retardant performance was achieved. Obviously, this novel flame retardant system paves new possibility for the high performance nonhalogen flame retardant polymeric materials and should also be applied to other polymers.