This paper introduced an explosion accident of 500 kV SF6 circuit breaker in Xingren converter station

the structure of breaking unit

theory of interruption and action process about the SF6 circuit breaker was discussed

combining with the practical situation

all possible factors of the accident is analysised.Finally the reasons of the accident were presented:the shafts in the T-mechanism were displaced caused by the two missing bearings after many opening and closing

a pin had sheared off by the excessive forces and finally breaked off from the mechanism;the arcing contacts could not contact after closing operation

a stable short arc was initiated across the arcing contacts

the pressure inside the breaking unit increased for the heated gas.At last

the interrupter exploded and led to a grid short circuit accident.To avoid similar accidents

this paper provided the corresponding proposal about quality control of manufacturers.