The open-close block of breaker is one of the serious defects in power dispatching. It may expand the range of outage and even cause power system instability after fault if not be treated in time. Analysis on system sending limitation before and after the open-close blocked of breaker is proposed to prove power grid has been operated into the state of emergency and power flow of the corresponding transmission section should be limited. Discussion on treatment of open-close blocked breaker in typical connection modes without outage of equipment is presented. Finally, risk analysis during the isolation of breaker is proposed and the corresponding prevention and control requirements are introduced to avoid local grid islanding or system instability after N-1 fault during defect treatment.