Low density polyethylene and linear low density polyethylene were used as basic materials, ammonium polyphosphate and diantimony trioxide were added into them as fire-retardant agent content to prepare fire-retardant system. The molding technological parameters and fire-retardant performance of the fire-retardant systems were tested. The results showed that with increase of fire-retardant agent content, the rotational speed of main screws needed decreases gradually and the pulling speed decreases accordingly; small change of the rotational speed of main screw causes the pressure of die increases sharply, and the real extrusion temperature increases accordingly; when the fire-retardant addition dosage is 40% , the fire-retardant level can reach FV-0.