Abstract: Aminopropyltriethoxysilane (KH550)-phenyltrimethoxysilan (Z6124) compound coupling agents with different components mixing ratios modified SiO₂/polytetrafluoroethylene (PTFE) composites were prepared, and the effects of mixing ratios of KH550-Z6124 components on the dielectric properties, water absorption rate and heat conduction properties were investigated systematically. Lichtenecker model was adopted to calculate the theoretical values of dielectric constant and dielectric loss of SiO₂/PTFE composites, and the theoretical values were compared with the experimental values. The research results show that when the mass ratios of KH550 and Z6124 to SiO₂ are 0.3wt% and 1.7wt%, the dielectric loss of KH550-Z6124 modified SiO₂/PTFE composites reduces from 1.7×10^-3 (Z6124 modified SiO₂/PTFE composites) to 1.0×10^-3, the water absorption rate reduces from 0.082 6wt% to 0.020 3wt% and thermal conductivity increases by 66%. The SEM microstructure analysis show that KH550-Z6124 modified SiO₂ particles disperse uniformly in PTFE matrix, and the interface connection is stronger. The experimental values of dielectric constant and dielectric loss of KH550-Z6124 modified SiO₂/PTFE composites are more closer to the theoretical values.