Abstract: The thermal barrier of nozzle diffuser was produced by twining carbon cloth/barium phenolic resin and glass fiber cloth/barium phenolic resin alternatively.Many products cracked due to delaminating during the process of natural storage after machining.To find out the failure cause,macro and micro observation,chemical composition analysis and thermal analysis were carried out.And simulation experiments were performed according to the process of soaking and twining.The results show that the weak bonding of carbon cloth led to interlayer cracking.Local free phenol content was higher in the process of presoaking and presolidifying,and ferric oxide was introduced during the twinning process.As a result,the fiber surface blued due to blue complexation reaction during the solidifying process,degrading the interface bonding strength.Finally,the thermal barrier cracked under internal stress and cutting stress.In accordance with this fault,prevention measures are proposed.