Abstract: An intumescent waterborne fireretardant coating for wood was prepared using the blend of melamine ureaformaldehyde resin(MUF) and polyvinyl acetate resin(PVAc) as filmforming resin, and the mixture of guanylurea phosphate(GUP), ammonium polyphosphate(APP), melamine(MEL) and pentaerythritol(PER) as intumescent fire retardant system. The fire retarding performance of three batch plywood specimens, which were painted with the prepared waterborne intumescent fireretardant coating(A), with the filmforming resin(M) and without any coating(S) respectively, was evaluated comparatively by cone calorimetry combined with thermogravimetric analysis(TGA) and Fourier transform infrared spectroscopy analysis(FTIR). The results showed that the heat release rate(HRR), the total heat release(THR) and the smoke release rate(SPR) of specimen A decreased more considerably than S and M. The highest value of mass of residual char(Mass) and markedly postponed time to ignition(TTI) were observed for specimen A. TGA analysis showed that GUP and APP played a catalytic charring effect in different temperature ranges, and the combination of two enhanced fire retarding performance of the coating by synergistic effects. FTIR analysis shows that the coating layer of A is thoroughly carbonized, further indicating that GUP-APP-MEL-PER is the effective fire retardant system of MUF-PVAc mixed resin.