Abstract: In this study, ureaformaldehyde resin was modified by polyvinyl formal (PVF). And mix the modified resin with stone powder to prepare the composite materials. The results showed that, after adding PVF to modified ureaformaldehyde resin, the pH value and viscosity were no significant changes with increasing the amount of PVF, but the free formaldehyde content was proportional to the amount of PVF. With 20% addition amount of PVF, the bending strength of the composite increased significantly to 1711MPa. And compared to the 5% addition amount of PVF there was a 6 times increased of bending strength. Combine to the SEM images, integration of ureaformaldehyde resin and powder particle surface was the highest degree when PVF amount was 20%.We can see that the degree of integration between the two surfaces was the main factors of the composite material’s bending strength.