The invention discloses temperature-stable microwave dielectric ceramic Li2SrSnO4 with high quality factor and low dielectric constant and a preparation method thereof. The preparation method comprises the following steps: (1) weighing original powders of Li2CO3, SrCO3 and SnO2 with purity being 00.9 wt% and above according to composition of Li2SrSnO4; (2) carrying out wet ball-mill mixing on the raw materials in the step (1) for 12 h by using distilled water as a ball-milling medium, drying, and presintering in the air atmosphere of 1,150 DEG C for 6 h; and (3) adding a binder into the powder prepared in the step (2) and granulating, conducting compression moulding, and finally sintering in the air atmosphere of 1,200-1,250 DEG C for 4h, wherein a polyvinyl alcohol solution with mass concentration of 5% is used as the binder and polyvinyl alcohol accounts for 3% of total mass of the powder. The prepared ceramic has good sinterability at 1,250 DEG C, dielectric constant reaches 24.1-25.5, quality factor (Qf) value reaches up to 76,000-106,000 GHz, and temperature coefficient of resonance frequency is small. The product has great application value in the industry.