Ba(Mg1/3Nb2/3)O3–MgO composite ceramics were prepared by solid-phase method. The ceramic exhibited the 1:2 ordered structure. By adding a proper amount of MgO, the permittivity decreased rapidly compared with other Ba(Mg1/3Nb2/3)O3-based ceramics. The Q × f values of the samples were greatly improved by nano-silica. Raman spectra showed that the permittivity and Q × f value showed a strong correlation with Raman shift and full width at half maximum of the A1g(O) phonon mode, respectively. The Raman shift of A1g(O) was consistent with the variation trend of permittivity. And the full width at half maximum of the A1g(O) phonon mode had a negative correlation with the Q × f value. The results showed that upon adding 1.5 wt% nano-silica to the ceramics, the ceramics sintered at 1550 °C for 5 h had the lowest Raman shift and the narrowest full width at half maximum, achieving the best microwave dielectric properties: εr = 22.22, Q × f = 80,436 GHz, τf = – 5.89 ppm/°C.