 Former studies on the theoretical model implies that TENG can be considered as a voltage source combining with a capacitor in series, of which the capacitance varies during operation.Based on the capacitive property, the assessment method is developed by charging the target TENG (TENG1) at different displacement x to measure the breakdown condition.Another TENG (TENG2) is added as the high-voltage source to trigger the target TENG to approach the breakdown condition.