Abstract: The stability of phases in the Ti3SiC2-TiSi2-TiB2composites prepared by argon arc deposition during the high temperature annealing in argon was analyzed in this study. The results showed that the Ti3SiC2phase was stable during annealing at 1 450 ℃ in argon, but in-situ synthesized solid solution phases such as TiSi2Cxdecomposed through atom diffusion during annealing. The transformed products were mainly composed of stable Ti3SiC2and a small amount of SiC. After annealing, the volume content of Ti3SiC2in the sample increased by 4.8% comparing with non-annealing. The thermodynamic calculation results showed that the reaction mechanism through atom diffusion during annealing was TiSi2Cx→Ti3SiC2+SiC. The atom diffusion reaction model of the Ti3SiC2-TiSi2-TiB2composites during annealing was proposed. The annealing experiment analysis results showed that the tungsten argon arc deposition combined with annealing process could improve the whole thermal stability of Ti3SiC2-TiSi2-TiB2composites.