The purpose of the invention is to provide a fixing method for a thick and large size cavity ceramic core, the fixing method is characterized in that firstly, a thick and large size cavity ceramic core is filled with coarse particle ceramic powders to strengthen the high-temperature performance of the core, then a ceramic rod bonded together with the ceramic core is inserted into two ends of the ceramic core to fix the ceramic core, a free end is arranged on the surface of the portion, exposed to the ceramic core, of the ceramic rod, and the ceramic rod is used for fixing the ceramic core in adie shell. The fixing method can meet the preparation requirement of single crystal/directional hollow turbine guide blades.