The invention provides a halogen-free flame retardant composition for ethylene propylene rubber and a preparation method of the halogen-free flame retardant composition. The flame retardant composition comprises the following components in percentage by weight: 65-75% of pentaerythritol phosphate, 15-25% of zinc aluminate, 3-7% of red phosphorus and 3-7% of dipentaerythritol. By adopting the flame retardant composition provided by the invention, a halogen-free flame-retardant ethylene propylene rubber material of which the hardness is less than shore A 60 degrees, the vertical combustion class can reach V0 class, the oxygen index is not less than 30%, the smoke density is less than 200, and the physical and mechanical properties are good can be prepared.