Low density polyethylene and linear low density polyethylene (LDPE/LLDPE (60wt.%/40wt.%))as basic materials, intumescent flame retardant ammonium polyphosphate (APP) was added into them to obtain fire retardant systems. The molding parameters, fire retardant properties, mechanical properties and processing properties of samples were examined. It was showed the rotational speed of main screw was 28-34rad/min. when samples were molded, cylinder temperature was 185-195°C, mold temperature was 85-115°C, preheating time was 5-10min and filling time was 8-21s. APP had good fire retardant and smoking suppression functions. Adding 30% (wt.%) APP can obtain grade of FV-0. With APP content increasing, the mechanical and processing properties of materials decreased.