High-pure Ti3(Si,Al)C2 solid solutions were synthesized by using Ti, Si, Al and TiC powders in the range of 1473K to 1773K. The microstructures and chemical compositions of all samples were characterized by X-rays diffraction (XRD) and scanning electron microscope (SEM). Microstructural analysis and mechanical properties test demonstrated that the Ti3(Si,Al)C2 solid solutions exhibited highest relative density and mechanical properties when synthesized at 1773K. In addition, it was worthy noted that experimentally determined lattice parameter c of Ti3(Si,Al)C2 crystal decreased with the increasing of sintering temperature. The contents of Si and Al elements in solid solution were conducted by Vegard’s Law. Gibbs energy differences (△G) of substitution process of Si (Si replace Al atoms) in Ti3(Si,Al)C2 solid solutions at different temperatures were also listed. With the increase of temperature, the △G value was negative and decreased gradually, which means that the transformation from Ti3(SipoorAlrich)C2 to Ti3(SirichAlpoor)C2 was spontaneous and had a greater tendency in higher temperatures. By combined the experimental and calculational data, a possible mechanism of this transformation was determined.