From the point of view of the operating experience combined with the 500kV system features the points which should be taken into consideration for the reliability of 500kV circuit breaker will be stated. For example: the connection layout and guality of the monitoring system of SF6 reme importance of the rustproof technology; the selection philosophy of the gas; the ezt-operating mechanism; some actual problems of the promotion of hte reliabil-ity of the hydraulic operating- mechanism. At last the nesessity of the parallel bredking and the feasibility of the development of 500kV GIS will also be stated.