Abstract: Low-density ablative thermal protection material is a key candidate material for spacecraft thermal protection systems. Its excellent high-temperature mechanical properties are the key to structural integrity of thermal protection structures under aerodynamic thermal loading. In this paper, the low-density ablation thermal protection composite of multiphase fibers reinforced phenolic resin composite was used to carry out compression experiments at high temperatures to obtain the variation law of the compressive strength with temperature. The influence of force load, pyrolysis and oxidation reaction on compressive strength was analysised by thermogravity and SEM. Two kinds toughening mechanisms of soft phase carbon layer bridging and fiber debonding and pull-out are revealed, which provides experimental data support for the application of the composite in thermal protection systems.