Li2Mg3Ti1-X(Mg1/3Ta2/3)(X)O-6 (x = 0.00, 0.05, 0.10, 0.15, 0.20) solid solution ceramics were prepared by the conventional solid-state reaction method. Rietveld refinements, Raman spectra, infrared spectra, polarizability and bond energy were used to research the changes of microwave dielectric properties of these solid solutions. With the increase of x values from 0 to 0.2, dielectric constants (epsilon(r)) gradually increased, which could be explained by the variations of the polarizability, infrared resonant modes and Raman vibration modes. The variations of the quality factor (Qf) could be explained by the changes of the bond valences. The temperature coefficient of resonant frequency (iota) correlated with the bond energy of Ti-O bonds. A small quantity of (Mg1/3Ta2/3)(4+) can obviously improve the microwave dielectric properties. Excellent microwave dielectric properties of epsilon(r) = 14.70, Q.f = 200,600 GHz and iota(f) = -11.83 ppm/degrees C were obtained for Li2Mg3Ti0.95(Mg1/3Ta2/3)(0.05)O-6 ceramic sintered at 1550 degrees C.