The thermal decomposition behavior, combustion behavior and pyrolysis behavior of expandable polystyrene（EPS）, extruded polystyrene（XPS） and polyisocyanate polyurethane（PIR PU） were investigated by thermogravimetric analysis（TGA）, cone calorimeter coupled with Fourier transform infrared spectroscopy（CC FTIR） and pyrolysis gas chromatograph mass spectrometer（GC MS）. Results of TGA indicate that initial decomposition temperature of PIR PU is significantly lower than that of EPS and XPS; thermal decomposition behavior of EPS and XPS is very similar; at high temperature, compared with EPS and XPS, PIR PU is with much more char. From results of CC FTIR, the values of heat release rate（HRR）, total heat release（THR）, smoke production rate（SPR） and total smoke production（TSP） of PIR PU are significantly lower than that of EPS and XPS, and time to ignition（TTI） of PIR PU is shorter than that of EPS and XPS; the toxic gases such as CO and HCN are detected in fire effluents of PIR PU, EPS and XPS, fractional effective dose（FED） values suggest that fire hazard of the toxic gases in fire effluents of PIR PU is the most serious. Results of pyrolysis GC MS indicate that isocyanate derivatives, aniline derivatives and chlorine containing flame retardant in pyrolysis products of PIR PU are the main reason for the presence of HCN and HCl in fire effluents, and aromatic derivatives in pyrolysis products of EPS and XPS lead to much smoke.