The invention relates to a ceramic core, in particular to a water-soluble ceramic core and a preparation method thereof, which can be used in investment casting of a casting with a complex cavity structure or a hollow casting with casting temperature of not greater than 900 DEG C. The water-soluble ceramic core is obtained by specifically taking fused corundum powder, zircon sand and sodium chloride particles as main body materials and NaCl solution and polyethylene glycol as adhesives through a specific mixing process by using low-temperature drying and a high-temperature roasting process. According to the water-soluble ceramic core, not only is the strength of the core guaranteed, but also the core has good moldability; and the water-soluble ceramic core has the advantages of convenience and quickness in operation (the core is only required to be washed with clear water and can be easily removed in a short time), no pollution, no need of special equipment, no damage to the casting and the like.