Thermal shock stability for ZrB2-SiCp-Graphite(ZSC) and ZrB2-SiCp-AlN (ZSA) was investigated by water quenching test. It indicated that ZSC may provide more stable thermal shock properties. As shown by SEM of ZSA, surface cracks appeared after it was cooled from 1200 , due to thermal shock instability of the material. Residual flexural strength of ZSA was improved by crack healing after it was cooled from 1450 . However, no surface crack appeared for ZSC after water quenching test. It provided a potential method for improving thermal shock stability of zirconium diboride ceramic matrix composites by introducing proper quantities of graphite.