The invention discloses a sealing strip which takes EPDM as the host material and the preparing method, which is characterized in that the composition contains the following constituents (expressed by wt percent): EPDM 26 percent, zinc oxide 1-1.5 percent, stearic acid 1-6 percent, polyethyleneglycol 0.5-1.6 percent, hydrafil 10-32 percent, zinc borate 5-16 percent, orthophosphoric lipid 3-16 percent, black carbon 7-20 percent, paraffin oil 7-21 percent, calcium oxide 2-5 percent, sulfur 0.25-0.5 percent and accelerant 0.65-1.5 percent. The invention ensures the mechanical performance and extrusion performance, is convenient for extrusion, adopts the hydrafil, the zinc borate, and a inflaming retarding system; is the most realistic non-halogen inflaming retarding; can produce a lot of crystal water on the surface of the burning substance; can separate the burning substance from contacting oxygen, and then can perform the inflaming retarding effect; can inhibit the gases produced by the burning substance, accordingly does not produce smog.