Abstract: Pentaerythritol and ammonium polyphosphate were surface-modified with tetraethoxysilane to prepare a series of intumescent flame retardants (IFR). The surface modification effect was confirmed by FTIR and TGA analysis. Nano Lanthanum Oxide (La2O3) were added into the modified flame retardants as a synergistic additive for flame retardancy and then melt blended with polypropylene (PP) to prepare the hydrophobic flame-retardant PP. The modification technology, the flame retardant and mechanical properties of polypropylenes were investigated. The results indicated that the hydrophobic properties of the modified PP were improved, and their flame-retardant and mechanical properties were improved considerably with the addition of La2O3.