More than 5000 A circuit breaker is usually each phase by multipole structure of parallel double terminal derivation, for above 5000A universal circuit breaker normal work shows the current is significantly greater than the measured current situation, the display difference is usually more than the accuracy of the manufacture gived. In this paper, through the theoretical analysis and the actual test, Through the theoretical analysis of the circuit breaker inside and the connection between the mutual sense and selfinductance phenomenon, it is found that the impedance of each pole of the circuit breaker is not exactly the same, the value of the load current between them is not equal, there is a significant phase angle between the load currents at different poles at the same phase, the phase angle is about 32 °. Because of the mutual inductance and selfinductance between the internal and external loads of the circuit breaker, the display is larger than actual current and the difference is about 5%.