In this paper, we studied the properties of polytetrafluoroethylene (PTFE) based and Li2Mg3SnO6 (LMS) filled composites. The LMS powders were synthesized by one synthetic process and modified by C14H19F13O3Si(F8261). The content of modified LMS changed from 26 to 66 wt%. XRD and TEM were employed to investigate the crystal phase of obtained LMS. The analysis of XPS and Contact Angle were conducted to study the surface characteristics of F8261 modified LMS. The morphology, microstructure, dielectric properties of PTFE based composites filled with untreated LMS and modified LMS were investigated in detail. Further, various theoretical models were put forward to discuss the dielectric constant of the composites. At last, the modified LMS filled PTFE composites exhibited reliable dielectric constant (epsilon(r) = 3.61), acceptable dielectric loss (tan delta = 0.002), stable frequency dependence of dielectric constant and low temperature coefficient of dielectric constant (tau(epsilon) = 9.42 ppm/degrees C) at filler loading of 46 wt% LMS.