Samples were prepared based on the chemical composition of Ru porcelain celadon glaze unearthed from Qingliangsi site. High-temperature microscopy, scanning electron microscopy, and colorimeter were employed to study the influence of calcium/potassium molar ratio in the glazes on firing temperature range, microstructure and coloration. The results show that chromatic a^* value and gloss of the glazes first decrease and then increase, while b^* value does the opposite with calcium/potassium molar ratio decreased gradually from 8.70 to 3.45. When calcium/potassium molar ratio is 5.08, the glaze characteristic shows a sudden change, showing a semi-matte surface, and the color is similar to that of unearthed samples. The microstructures are mainly the changes of morphology of anorthite and phase separation. When calcium/potassium molar ratio is in the range of 8.70~6.47, the morphology of anorthite is columnar, acicular and lamellar, and the phase separation structure gradually changes from isolated droplet to cotton wool, and the average size decreases. When calcium/potassium molar ratio is in the range of 5.08~3.45, the surface tension of the glaze melt begins to fluctuate greatly, the form of dendrite begins to appear, and the secondary branches appear, which decreases the “clarity” of the glaze. When the firing temperature is below 1 170 ℃, glaze with calcium/potassium molar ratio of 8.70 exhibits good melting effect due to its lower softening temperature, while the other samples show poor melting effect due to their higher softening temperature. When the firing temperature is between 1 170 ℃ and 1 220 ℃, glaze with calcium/potassium molar ratio of 5.08 has a relatively wide firing range, with a relatively large amount of liquid phase and changing smoothly. The color is relatively stable and glaze has a good melting effect, which can improve the color fluctuation issue in Ru porcelain celadon glaze caused by the narrow firing range.