The interface incompatibility between organic polymer and inorganic ceramic filler is a common phenomenon in polymer-based dielectric composites. In this paper, the Ar/CF4 plasma is used to modify the CaTiO3 particles, which improved the dispersion of CaTiO3 and its compatibility with polytetrafluoroethylene (PTFE). The findings demonstrate that growing argon (Ar) flow rate was beneficial to enhance discharge and increase fluorinated graft content. The modified CaTiO3/PTFE is uniformly distributed and has no serious agglomeration phenomenon, which effectively improves its dielectric characteristics. Modified CaTiO3/PTFE composite with 5 wt.% CaTiO3 has a dielectric constant of 2.32 whilst the dielectric loss reaches 2.8 × 10−3 at around 10 GHz.