||Theoretical and experimental study of the electrical fracture behavior of the dielectric materials, Soda-Lime Glass and Acrylic Glass (PMMA), was made in this work. The charge-free zone (CFZ) model proposed by Zhang et al. for the failure of conductive cracks in dielectrics, which was well verified by Wang’s experimental results of depoled piezoelectric ceramics PZT 4 and extended by Liu’s experimental results predicting the failure behavior of conductive cracks in piezoelectric ceramics, was applied as a failure criterion to the dielectric breakdown study of Soda-Lime Glass and PMMA. Experiments can use the failure criterion (CFZ model) to study the failure behavior of electrically conductive cracks (deep notches) in Soda-Lime Glass, but it is not suitable for PMMA from recent test results. According to the CFZ model for dielectric materials, the experiment result should be described by a straight-line function. The critical electric intensity factor under purely electric loading of Soda-Lime Glass was obtained using a straight line function to fit the combined results. The electric energy release rate was also found to be larger than the mechanical energy release rate in Soda-Lime Glass. With the dimple structure patterns appearing on the fracto-picture under combined tests, it proved that Soda-Lime Glass is also mechanically brittle and electrically ductile. However, for Polymer material, PMMA, this kind of failure criterion cannot be used to fit the critical electric intensity factor under purely electric loading. Some ductile properties also appeared on the fracture surface of PMMA under combined tests. It also proved that PMMA is mechanically brittle and electrically ductile.