Abstract: A kind of high-temperature resistant foam composites with relatively integrated structure after pyrolysis was prepared with ZrSi₂ particles filling boron-modified phenolic resin. The curing mechanism, high-temperature pyrolytic behaviors, compression performances before and after pyrolysis of foam composites were investigated with respect to ZrSi₂ particle mass fraction, and the strengthen mechanism of ZrSi₂ particles on pyrolytic products of foam composites was also analyzed. The results show that the introduction of ZrSi₂ particles does not affect the curing and crosslinking of boron-modified phenolic resin but induces chemical reactions with pyrolytic volatiles derived from boron-modified phenolic resin, which could increase the char yield and the compressive specific strength of pyrolytic products. When the mass ratio of introduced ZrSi₂ particles to boron-modified phenolic reaches 10%, there is the most significant improvement on the char yield and the compressive strength of pyrolytic products. After pyrolysis of ZrSi₂/boron-modified phenolic foam, ZrSi₂ particles are pinned on the cell walls of pyrolytic products as the secondary phase particles, part of pyrolytic volatiles are absorbed and translated into solid phase products by chemical reaction, and obviously decreased defects increase the mechanical property of pyrolytic products.