The reaction sintering, without calcination and following re-grinding, has been paid increasing attention. Non - stoichiometric Li2Mg3Sn1 − xO6 (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics were successfully gained through reaction sintering process in the study, and its phase composition, morphology and dielectric characteristics were studied. This XRD patterns of Li2Mg3Sn1 − xO6 samples prepared after sintering at 1,305 ℃ for 6 h indicates that green bodies are mainly composed of Li2Mg3SnO6 phase, accompanied by the second phase of Mg2SnO4. A host of pores, elliptic - like grains and wrinkle - like grains were visibly observed from the SEM images of Li2Mg3Sn1 − xO6 ceramics, which is because of the severe volatilization of Li elements at high temperature. The apparent density, relative permittivity, quality factor and temperature coefficient of resonant frequency of samples will be devastate owing to porous morphology and Mg2SnO4 phase to a large extent. Finally, when x = 0.08, Li2Mg3Sn0.92O6 ceramics have optimal dielectric performances: εr = 9.133, Q×f = 55,429 GHz, τf = -36.1 ppm/℃.