The principle of the Isothermal Capacitance Transient Spectroscopy[ICTS] were explained to measure the electronic trap levels in oxide ceramics. The measurement apparatus and the theory of the ICTS were described in detail. The trap energy evaluation was performed for the ZnO varistor and BaTiO3 ceramics. The grain boundary interface trap levels were detected at -5$0^{circ}C$~6$0^{circ}C$ in the case of ZnO varistor and PTCR samples, and the bulk trap levels were detected at 2$0^{circ}C$~60~ in BaTiO3. The trap energy levels of the above samples could be directly determined by ICTS measurement.