The prefab-core method is favored in the fabrication of multi-layer ceramic cores for its advantages of process simplification and cost reduction. As the inner cavity of a ceramic core, a fusible core was prepared in this research with polyethylene glycol (PEG) as the plasticizer, graphite and quartz glass powder as the fillers. The ceramic core was prepared by secondary injection molding method, and co-debinding with fusible core was achieved. The effects of molecular mass of PEG on the properties of fusible core slurry and green body were studied. The results showed that the molecular mass of PEG played a minor role when molecular mass was less than 2 000, yet the performance of the green body would become poor due to increased defects when the molecular mass exceeded 2 000. That is to say, the fusible core prepared with PEG2000 had the best performance:the flexural strength, heat deflection and surface roughness of the fusible core were 13.0 MPa, 2.94 mm, and 1.18 μm, respectively. The co-debinding behavior of the ceramic core/fusible core was also investigated. After debinding and sintering, the fusible core was burned out and the inner cavity of multi-layer ceramic core was formed. The structure integrity and dimensional accuracy of the ceramic core were not influenced by the removal of the fusible core. The dimensional accuracy and inner surface roughness of ceramic core were less than ±0.15 mm and 1.808 μm, respectively, which met the requirements of high temperature casting.