By evaluating the health status of high voltage circuit breaker， and considering these statuses in power transmission risk assessment， a new method for the power transmission risk assessment is presented， in which the operation status of high voltage circuit breakers is considered. A new outage probability model for power transmission risk assessment is developed by involving the effects of operation data of high voltage circuit breakers. Transmission risk is then calculated based on the model. The IEEE-RTS 79 system is used to calculate the adequacy risk of transmission system， and the demonstration shows that the method proposed is scientific and feasible.