In order to reduce the erosion effect of propellant, porous urea-formaldehyde resin microspheres were synthesized by stepwise polymerization of urea and formaldehyde without introducing templates and structure-directing agents. Nano-sized TiO₂ particles were deposited on the pores by sol-reflux method, and composite microspheres were formed as erosion inhibitors. SEM and particle size analysis showed that there were obvious mottled nanopores on the surface of urea-formaldehyde microspheres. Combined with FT-IR and XPS analysis, it was determined that nanopores could be used to deposit high purity nano-TiO₂. The particle size distribution of urea-formaldehyde/TiO₂ composite microspheres was in the range of 7-30 μm. Thermal analysis results showed that the inorganic content of the composite microspheres was about 6%. The composite microspheres exhibited good compatibility with the propellant, which did not affect the thermal decomposition of the propellant and was beneficial to improving the thermal stability of the propellant. The erosion inhibition performance of the composite microspheres was verified by the semi-closed bomb test. When the composite microspheres had a mass ratio of 3.4% relative to the propellant, the effect was the best and the erosion-reducing efficiency was 20.5%. This composite material is expected to be applied to the modification of standard propellants and the design of new high-energy propellants.