Provided are a room temperature crosslinked type halogen-free flame retardant resin composition and a method of preparing the same. Specifically, a room temperature crosslinked type halogen-free flame retardant resin composition according to the present invention including a polyethylene resin, a olefin-based elastomer, a metal hydroxy compound, a radical initiator, a crosslinked type alkoxysilane-based compound, a condensation catalyst of the crosslinked type alkoxysilane-based compound, and one or more crosslinking aids selected from the group consisting of an aliphatic acid and an aliphatic acid metal salt, and a method of preparing the same are provided. Further, a compound material and a masterbatch which are compositions for preparing the room temperature crosslinked type halogen-free flame retardant composition, and methods of preparing the same are provided.