The lithium-based silicate microwave dielectric ceramics with ultra-low permittivity show great potential as substrate materials in the fifth-generation wireless communication technology. However, the residual stress caused by higher sintering temperatures leads to increased dielectric loss, thereby deteriorating the microwave dielectric performance. In this work, B³⁺ was introduced into LiAlSi₂O₆ ceramics to reduce Al³⁺ content, aiming to improve their sintering temperature and microwave dielectric performance. LiB_xAl_1-xSi₂O₆ (0≤x≤0.20) microwave dielectric ceramics were prepared using a combination of solid-state reaction and cold isostatic pressing techniques. Effects of B³⁺ doping on the sintering characteristics, phase structure, microstructure, and microwave dielectric properties of the materials were characterized. The results show that with a gradual increase in the doping concentration, sintering temperature of the ceramics decreases significantly from 1400 to 1000 ℃. Meanwhile, the relative permittivity (ε_r) decreases from 3.95 to 3.69, the quality factor (Q×f) increases significantly from 24300 to 30560 GHz, and the temperature coefficient of resonant frequency (τ_f) increases from -45.9×10^-6 to -20.9×10^-6 ℃^-1. Specifically, the change in ε_r is mainly influenced by intrinsic polarization, lattice vibrations, and covalent bond strength of the material; the improvement in Q×f is closely related to the increase in packing fraction (PF) and the decrease in damping coefficient; the increase in τ_f is strongly correlated with the bond valence of oxygen (V_O). Furthermore, the composition with x = 0.20 exhibits the best microwave dielectric performance with ε_r = 3.69, Q×f = 30560 GHz, and τ_f = -20.9×10^-6 ℃^-1. Findings of this study on LiB_xAl_1-xSi₂O₆ provide important theoretical guidance and practical insights for development and application of high-performance microwave dielectric ceramics in the future.