A CaO–Al2O3–SiO2 (CAS)-based glass interlayer was developed for joining of porous alumina membrane tubes with dense alumina in this work. The results indicated that the interfacial microstructure of the joint was highly sensitive to the quench rate from the joining temperature, which rendered crystallization of CaTiSiO5 at a fast quench rate but CaAl2Si2O8 at a slow quench rate due to the interfacial reaction between the CAS glass interlayer and the substrate. An extra crystallization treatment during quench, i.e., dwelling at 800°C–900°C for 2 h, produced a multiphase interlayer consisting of LiAlSi2O6, CaTiSiO5, and CaAl2Si2O8. All joints were evaluated by the thermal shock test. The results showed that the LiAlSi2O6-containing joint interlayer had much lower thermal shock resistance than those without LiAlSi2O6.