Abstract: The technological process and parameters of preparing expandable polystyrene(EPS) in laboratory scale were investigated. The foaming performances of EPS foam coated with prepolymer of melamine-formaldehyde(MF) together with ammonium polyphosphate and zinc borate(ZB)were characterized. The flammability and the thermal properties were evaluated using limiting oxygen index(LOI) test and thermogravimetric analysis (TGA)，respectively. It indicated that coating was an effective method to improve the flame retardancy of EPS foams:the LOI value was increased from 18.0% to 22.6%;the char residue increased 85%;shrinkage was significantly reduced during burning process;combustion rate was also reduced to 51.7%.The presence of ZB which acted as a dehydration catalyzer，could increase both the amount and strength of char residue and hence further improved the flame retardancy.

Key words: expandable polystyrene, pre-polymer of melamine-formaldehyde, coating;flame retardant