Electrical endurance is one of the main parameters for the condition assessment of circuit breakers. To realize the on-line monitoring of electrical endurance for the circuit breakers under 10 kV voltage level in several substations， a new type of monitoring system is developed， in which a method proposed is used to calculate the electrical endurance with the measured current at the 10 kV side of power transformer and position change information of circuit breakers. The monitoring system has the characteristic of low cost and can be installed even under charged state.