Mechanical failure is an important reason for electrode degradation, especially for the anodes with large volume change during the electrochemical cycles. Plenty of studies prove that nanostructure materials under the critical size would significantly improve the stability of the electrodes. The commercial electrodes are inevitable defective during preparation, and the defect induced fractures will reduce the critical size. However, the mechanisms of this phenomenon are still unclear and lack of the support of precise experiments. In the present study, silicon islands under critical size are prepared and different types of defects with various curvatures are designed in the island electrodes. The in-situ experiments are employed to observe crack appearance, and the defects with higher curvatures are found to fail earlier than the others. Furthermore, the finite element analysis is used to quantitatively calculate the stress evolution around each defect. The results also show that the safe (no fracture) area of the electrodes is reduced by the defects with high curvature, and the critical failure state of charge could be obtained by the experiments and simulation data.