Abstract: Studied an intumescent flame retardant coating based on an acrylic resin system, into which tri(2,6,7-trioxa-1-phosphabicyclooctane-1-oxo-4-methanol)phosphate(trimer) or modified trimer,ammonium polyphosphate(APP) and melamine(MN) were incorporated.The fire resistant time,smoke density and thermostability of the coatings were characterized by fire protection test,smoke chamber test and thermogravimetric analysis(TGA).The morphology of intumescent char,elemental composition and chemical states of the char residue were investigated using high magnification zoom microscope and X-ray photoelectron spectroscopy(XPS).The results showed that the backside temperature of the modified trimer-APP-MN coating had a decrease of 60 ℃,the maximum smoke density had a decrease of 58% at a coating thickness of 0.5 mm and burning time 11 min;the thermostability had an increase of 65 ℃ compared with the traditional ammonium polyphosphate-pentaerythritol-melamine(APP-PER-MN) coating.