Diphenyldiphenylethynylsilane monomer (DPDPES) was synthesized with ethyl bromide, diphenyldichlorosilane and phenylacetylene by Grignard reaction. The molecular structure was characterized by FTIR and ¹H-NMR spectroscopy. The polymer of polydiphenyl(diphenylethynyl)silane (PDPDPES) was also prepared by thermal polymerization. Non-isothermal thermal decomposition process of PDPDPES was studied with TG-DTG technology via model method to get thermal decomposition function and the corresponding mechanism which was further verified by model-free method. Results show that the apparent activation energy and the pre-exponential factor are about E_a=245.37kJ/mol and lgA=13.78s^-1 obtained by six different kinetic methods, respectively. The mechanism of functions are f(α)= 10/23 ·(1-α)·[-ln(1-α)]^-1.3 and g(α)=[-ln(1-α)]^2.3。