Although A-site codoping of alkali metal and rare-earth elements are known to effectively promote the d(33) of CaBi2Nb2O9 (CBN), its thermal depoling behavior cannot be well promised. In this work, piezoelectricity of CBN was effectively promoted by (NaCe) modification, and its thermal instability was caused by the lattice evolution from orthorhombic structure to pseudo-tetragonal structure during thermal depoling process. A-site vacancies could induce pseudo-tetragonal distortion in Ca-0.92(Na0.5Ce0.5)(0.08)Bi2Nb2O9 ceramic, which obviously enhanced the thermal stability of lattice by reducing the rotation of the Nb-O octahedron during the thermal depoling process, as compared with orthorhombic structure, thereby weakening the swing of spontaneous polarization (P-s) and promoting the thermal depoling performance. Consequently, good thermal stability was obtained (remained 92% of initial d(33) after depoling at 600 degrees C). Moreover, dominant role of oxygen vacancies in the electrical conduction and relaxation process promised that the introduction of small amount of A-site vacancies would not influence the electrical properties obviously.