Four breaker breakdown are discribed in this paper.Either insulation defect or mechanical error may cause breaker breakdown of circuit breakers.And the faults cannot be cleared automatically when breakdown happened due to the system voltage.The fault current of breaker breakdown is quite small than the short circuit current as there is no phase to ground fault.None protection operates immediately when breaker breakdown happens and the electric-arc buries between breakers for few seconds.The circuit breaker and the SF6 gas may be damaged during the arc buries.The protecting devices do not operate until the breakdown between the contacts becomes a phase-to-ground and the fault current increases rapiddly.The circuit breakers of EHV transmission line with parralle reactor and breakers of generator-transformer unit have higher risk of breaker flashover than other circuit breakers.The reason of breaker flashover of circuit breakers are analyzed in this paper.Breaker flashover protection of circuit breaker are introduced to protect the circuit breakers from damagement during breaker breakdown faults.The protection setting and time delay of breaker flashover protection for circuit breaker of transmission lines and generator-transformers are discussed respectively.