The abnormal breakage of the closing resistance inside the ACF circuit breaker in the high-voltage direct current transmission converter station affects the stability of the power system, so the study of the abnormal breakage of the closing resistance of the ACF circuit breaker in the converter station is of great significance. This paper describes the mechanics and electric field simulation principle, based on the surface of the non-completely smooth case of the closing resistor stress distribution simulation study, which found that the closing resistor contact position of the maximum stress with the increase of the degree of non-smoothness and increase, when it reaches a certain level will cause the resistance piece of the abnormal breakage. The electric field simulation of the falling process of the broken fragments found that the falling of the resistor fragments caused the electric field distortion inside the circuit breaker, which led to the surge of the electric field, causing partial discharge and secondary damage to the closing resistor.