Abstract: The hollow glass microspheres(HGM) were used as additives to prepare a series of HGM/rigid polyurethane foam(RPUF) composites by one-step water-blown method. SEM, TG, limiting oxygen index(LOI) and horizontal combustion were applied to investigate the cell structure, char layer morphology, thermal stability and flame retardancy of the HGM/RPUF composites. The universal material testing machine was applied to study the compressive strength and compressive elastic modulus of the HGM/RPUF composites. Thermogravimetric analysis-Fourier transform infrared spectrophotometer(TG-FTIR) was applied to investigate the gaseous phase products of the HGM/RPUF composites. The results show that the HGM work as nucleating agent, which can reduce the pore diameter of the HGM/RPUF composites. In combustion, the HGM particles migrate to the surface of the char layer, promoting the formation of the compact char layer. When 5.4wt% of HGM were added, the compressive strength and compressive elastic modulus of the HGM/RPUF composites are increased to 0.14 MPa and 4.53 MPa, respectively, which are increased by 37.30% and 67.16% compared with those of the RPUF. At the same time, it is found that the HGM can significantly inhibit the release of toxic CO in combustion process, enhancing the fire safety of the HGM/RPUF composites.