[Objective] Grouting has been recognized as an effective solution for water inrush treatment in underground engineering. Organic grouting materials such as polyurethane (PU) are strongly adhesive but expensive,whereas inorganic grouting materials such as waterglass (WG) are cheap but have low elasticity. To improve the performance of polyurethane grouting materials,we investigated the influence of waterglass content on the macroscopic and microscopic properties of polyurethane. [Methods] Polyphenyl polymethylene polyisocyanate (PAPI),waterglass,and polyether polyol were used as the basic raw materials,and the inorganic/organic hybrid method was adopted to prepare polyurethane foam grouting material modified by waterglass. The influence of waterglass content by weight (0,20%,40%,60%,80%) on the foaming rate,density,and compressive strength of the modified polyurethane was investigated. A fitting relationship between polyurethane density and elastic modulus was established. Scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were used to measure the influence of waterglass content on the cross-sectional morphology and thermal stability of materials. [Results] (1) Macroscopic property results showed that,with increasing waterglass content,both the foaming rate and compressive strength first increased and then decreased. When the waterglass content was 20%, the foaming rate and compressive strength reached maximum. Under this condition, the foaming rate was 2 684%, and the compressive strength at 7 d was 38.9 MPa. In addition, the heat released by the reaction increased the instability of the cell structure and even caused cell collapse, resulting in decreases in foaming rate and compressive strength. Notably, when the density changed from 1.102 g/cm³ to 0.959 g/cm³, the compressive strength of materials decreased by approximately 70%. Based on the experimental results, the fitting relationship between the density and elastic modulus of the modified polyurethane was obtained as E∝ρ^1.8.(2) The results of scanning electron microscopy showed that, with increasing waterglass content, the smooth polyurethane surface was gradually covered by an amorphous inorganic phase surrounding the spherical cells. The structure of the materials eventually became loose and porous.(3) TGA results showed that the thermal stability of the modified polyurethane was better than that of pure polyurethane. The TG curve showed that when T<80 ℃, the thermal mass loss of the materials was only about 5%, indicating that the initial decomposition temperature of the materials was about 80 ℃. When T >600 ℃, the curve became stable, meaning that the modified polyurethane with waterglass content of 0, 20%, 40%, 60%, and 80% lost approximately 84%, 77%, 72%, 65%, and 53% of their mass, respectively. The curves then tended to stabilize, indicating that the incorporation of waterglass could enhance the thermal stability of polyurethane.(4) DTG (Differential Thermogravimetry) curve showed that the mass loss rate of polyurethane was significantly higher than that of the modified polyurethane. This was attributed to the fact that the inorganic components precipitated in the reaction system were encapsulated on the surface of polyurethane matrix. The presence of Si-O bonds increased the intermolecular forces, resulting in the need for more energy to cause thermal decomposition of the materials. Therefore, the addition of waterglass effectively reduced the thermal decomposition rate of polyurethane.[Conclusion] Polyurethane/waterglass (PU/WG) is an organic-inorganic hybrid material that has the advantages of both polyurethane and waterglass. Analysis of the relationship between waterglass content and the macroscopic and microscopic properties of the modified polyurethane shows that the addition of waterglass helps increase the foaming rate, compressive strength, and thermal stability of polyurethane. These findings offer data support for the performance improvement and system optimization of the modified oil-soluble polyurethane grouting materials.