ZrB 2-20%SiC (ZS) and ZrB 2-20%SiC-10%graphite (ZS10C) were fabricated by hot-press sintering method. A novel method was proposed to characterize material failure for heating up at the center of ultra high temperature ceramic. Thermal stress field was calculated under different center temperatures for ZS. It showed that the material would be failed when the center temperature was higher than 2300 °C. It was consistent with the experimental results. Holding percentage of residual strength for ZS10C was higher than that for ZS, which can be attributed to flake shape graphite for ZS10C. It indicated that the material with higher crack resistance would improve security when applied under high temperatures.