Abstract: By means of DSC, non-isothermal crystallization behavior of PTFE/SiO₂ composite at different thermoforming temperature is investigated in which part of micro-SiO₂ is replaced by nano-SiO₂.The results of DSC analysis show that when the thermoforming temperature is higher than 370℃, as degree of polymerization decreases, microstructure of the crystalline PTFE changes and performance of the composites deteriorates.The non-isothermal crystallization DSC analysis of composites indicates that their crystallization process includes both homogeneous nucleation and heterogeneous nucleation.When the substitution is less than 0.25%, the nucleation is enhanced.When the substitution is more than 0.25%, the nucleation enhancemont is not obvious for SiO₂ particle agglomeration and poor interfacial compatibility between the PTFE and SiO₂.