A cavity body can comprise a sand mold, a porcelain tube, a heat conducting body and a cavity, wherein the cavity is located inside the sand mold and is used for containing a poured casting, the heat conducting body is located inside the sand mold, comprises a crude sand porcelain tube upper contact surface and a casting lower contact surface which are arranged oppositely and further comprises a side contact surface, the crude sand porcelain tube upper contact surface comprises a porcelain tube accommodating area and a crude sand fixing area surrounding the porcelain tube accommodating area, the porcelain tube accommodating area of the heat conducting body is fixedly connected with the cylindrical hollow porcelain tube communicating with the outside of the sand mold, a dimple for accommodating a thermocouple is formed in the porcelain tube accommodating area, corresponding to the hollow part of the porcelain tube, of the heat conducting body, the outer surface of the porcelain tube, the crude sand fixing area of the heat conducting body and the side contact surface of the heat conducting body are closely contacted with the sand mold, the casting contact surface is consistent with the edge of the cavity in shape, and the casting contact surface of the heat conducting body is closely contacted with the casting after the casting is poured in a pouring cavity. An embodiment of the invention further provides a casting temperature measuring method for in-cavity ageing.