Abstract: Three types of surface modifiers, i.e. phenyl trimethoxy silane modifier (PTMS), solution of rare earth modifier (RES) containing PTMS (PTMS-RES) and RES solution, were used for the surface treatment of the milled glass fiber. The effects of the different surface treatment conditions on the dielectric properties, coefficient of thermal expansion and heat conduction properties of milled glass fiber reinforced milled glass fiber/polytetrafluoroethylene (MGF/PTFE) composites were investigated in detail, and FTIR spectra of RES, unmodified and modified of MGF, and the fracture surfaces were analyzed by SEM. The experimental results show that the dielectric properties, coefficient of thermal expansion and heat conduction properties of the MGF/PTFE composites filled with modified milled glass fiber are improved, compared with that of the MGF/PTFE composite filled with unmodified milled glass fiber. The effect of milled glass fiber with RES is superior to PTMS due to the effects of rare earth specific electronic structure and has a strong attraction to the anion, PTMS-RES is superior to RES in improving the interface and promoting the interfacial adhesion between the milled glass fiber and PTFE due to the effects of rare earth with PTMS.