The invention discloses temperature-stable microwave dielectric ceramic LiMg2V7O20 with an ultra-low dielectric constant and a preparation method of the ceramic LiMg2V7O20. The preparation method comprises the following steps: (1) weighing and proportioning Li2CO3, MgO and V2O5 original powder which have purities of 99.9wt% or above; (2) carrying out wet ball-milling mixing on the raw material obtained in the step (1) for 12h, drying and then presintering in a 750 DEG C air atmosphere for 6h, wherein the ball milling medium is distilled water; and (3) adding a binder to the powder obtained in the step (2), granulating, carrying out compression moulding, and finally sintering for 4h in a 800-850 DEG C air atmosphere, wherein the binder is a polyvinyl alcohol solution with a mass concentration of 5% and the addition amount of polyvinyl alcohol accounts for 3% of the total mass of the powder. The prepared ceramic has good sintering performance at a temperature of 850 DEG C or below; the dielectric constant reaches 16.4-17.3, the quality factor (QF) value is high up to 97000-143000GHz, and the temperature coefficient of resonance frequency is small, and thus the temperature-stable microwave dielectric ceramic LiMg2V7O20 with an ultra-low dielectric constant has extremely large industrial application value.