Secondary locking structure, connector and use method of connector

The invention discloses a secondary locking structure, a connector and a use method thereof, the secondary locking structure comprises a first connecting piece, a second connecting piece, a locking piece and a third connecting piece, the outer surface of the first connecting piece is provided with a lock catch, and the lock catch is provided with a locking structure A; a locking groove is formed in the second connecting piece, and a locking structure B is arranged in the locking groove; the third connecting piece is movably arranged on the first connecting piece, and the locking piece is provided with a locking part which can be inserted into a gap between the first connecting piece and the lock catch; the third connecting piece is provided with a first position on the first connecting piece, and at the moment, the third connecting piece enables the locking part of the locking piece to be located in the gap between the first connecting piece and the lock catch; the connector further comprises a plugging assem