The thermal degradation temperatures and the rate of char yields of homopolymers and coplymers of arylacetylenes were determined by thermogravimetry. The correlations between these properties and the composition and structure of polyarylacetylenes were also revealed. The more diethynylaromatic copolymer contains and the bigger cross link density，the higher the thermal degradation temperature and char yields. Char yields of copolymer of diethynylaromatic and phenylacetylene are much greater than that of the calculated data from their homopolymers.