Due to use of the intermediate relay in existing SF6circuit breakers gas low pressure block loop， there may not block the closes opening and closing loop caused by fault of intermediate relay or can not send out block signal immediately. In view of this problem， by comparing several typical circuit breaker manufacturers design advantages and disadvantages in the low pressure block loop， some improved methods are introduced， such as changing the block loops single normally-closed contact of intermediate relays to two normally-closed contacts， changing the block signals single normally-open contact to parallel two normally-open contacts， etc. The low pressure block and low reliability of signal-sending loop have been simply and effectively solved.