The graphite intercalating reaction with KMnO4 as oxidant, H2SO4 as intercalating reagent and sodium tetraborate (Na2B4O7.10H(2)O) as assistant intercalating reagent has been carried out to prepare a combined intumescent flame retardant consisting of expandable graphite and borate. The method of preparing combined expandable graphite (EG) with a high dilatability and feasible initial expansion temperature is confirmed as following: mass ratio of CKMnO4:H2SO4 (98%): Na2B4O7. 10H(2)O is controlled as 1.0:0.4:5.5:0.6. H2SO4 is diluted to 80 wt% before intercalation reaction, and the reaction last 40 mm at 40 degrees C. Initial expansion temperature and expansion volume of the EG are 155 degrees C, 515 mL/g, respectively; and its flame retardancy for linear low density polyethylene is also investigated. Addition of 30 wt% EG to the polymer can make the limiting oxygen index increase from 17.1 to 28.4%. The flame retardancy can be improved by addition of ammonium polyphosphate APP, and the limiting oxygen index of 70 LLDPE/10APP/20EG reaches 30.5%. X-ray powder diffraction analysis, thermal gravimetric and Fourier transform infrared analysis have been used to illuminate the retardancy mechanism. The intercalating borate can make EG show higher dilatability and flame retardancy.