In this study, low-temperature fired CaMg_1-xLi_2xSi₂O₆ microwave dielectric ceramics were prepared via the traditional solid-state reaction method. In this process, 0.4 wt% Li₂CO₃-B₂O₃-SiO₂- CaCO₃-Al₂O₃ (LBSCA) glass was added as a sintering aid. The results showed that ceramics consisted of CaMgSi₂O₆ as the main phase. The second phases were CaSiO₃ always existing and Li₂SiO₃ occurring at substitution content x > 0.05. Li⁺ substitution effectively lowered sintering temperature due to 0.4 wt% LBSCA and contributed to grain densification, and the most homogeneous morphology could be observed at x = 0.05. The effects of relative density, the second phase, and ionic polarizability on dielectric constant (ε_r) were investigated. The quality factor (Q × f ) varied with packing fraction that concerned the second phase. Moreover, the temperature coefficient of the resonant frequency (τ_f) was influenced by MgO₆ octahedral distortion and bond valence. Excellent dielectric properties of the CaMg_1-xLi_2xSi₂O₆ ceramic was exhibited at x = 0.05 with ε_r = 7.44, Q × f = 41,017 GHz (f = 15.1638 GHz), and τ_f = −59.3 ppm/℃ when sintered at 900 ℃. It had a good application prospect in the field of low-temperature co-fired ceramic (LTCC) substrate and devices.