Aiming at the problem that in certain cases, traditional failure protection settings of 220 kV circuit breaker cannot meet the fault clearing time requirements to keep system stable, based on the characteristics of 220 kV breaker failure protection, the factors affecting fault clearing time such as main protection action time, breaker opening time, arc extinction time and current element return time and their time boundaries are analyzed. The matching necessity of the two-stage of bus coupler breaker tripping, feeder retripping and adjacent breaker tripping is evaluated. The delay optimization scheme of circuit breaker failure protection considering critical limit clearing time of the system and lower limit time of failure protection is proposed, giving consideration of both failure protection and power system stability, and the calculation method of the fault duration is provided.