In the present report, the curing behavior of two thermoset resins containing silicon alkynyl group- PAR and PMR, and the correlation between the curing structure of resin and their thermal stability were investigated by FTIR, 13C NMR, DSC and TGA techniques. The IR and NMR results showed that the curing mechanism of PAR and PMR resin is different. Based on aromatic cyclization among alkynyl groups and Diels-Alder reaction, aromatic frame network structure constituted by benzene cycles and condensed aromatic cycles are formed in the PAR cured resin. Using additional reaction among Si—H group, alkynyl group and alkenyl group, saturated Si—C(sp3) network structure is formed in the PMR cured resin. The aromatic frame network structure and Si—C(sp3) network structure provide good thermal stability for PAR and PMR resin respectively. The thermal decomposition temperatures Td5 of both resins are above 600 ℃, and the residues percentages at 900 ℃ are above 85%.