Disclosed are an adapter (6) and an adapter assembly using the adapter (6). The adapter (6) comprises an adapter shell (13, 12, 11), wherein an adapter socket contact part (18), an adapter socket locking structure, an adapter plug contact part (14), an adapter plug locking structure, and a seal fit portion for being inserted into a corresponding connecting sleeve (4) in a sealing manner are arranged on the adapter shell (13, 12, 11), and the seal fit portion is located between the adapter socket locking structure and the adapter plug locking structure. The adapter and the adapter assembly using same have a waterproof function.