The invention relates to a method for preventing erroneous outlet of in-situ protection GOOSE messages, a protection device and a startup CPU. The protection device includes a startup CPU and a protection CPU. When the startup CPU determines that a failure occurs according to the collected analog quantity, a GOOSE message is not immediately output, but by further determining, the startup CPU determines whether a trip-out outlet message sent from the protection CPU and a trip-out forced issued signal are received, and when both the trip-out outlet message and the trip-out forced issued signal are received, the GOOSE outlet message is output, thus avoiding the problem that once the prior art determines that a fault occurs according to the collected analog quantity, a GOOSE outlet message isoutput so as to cause erroneous outlet of the GOOSE message. Therefore, the method for preventing erroneous outlet of in-situ protection GOOSE messages prevents misoperation of the protection device and has high reliability.