The invention discloses an air treatment and conveying system utilizing a traffic hole for inputting air in offshore underground engineering. The air treatment and conveying system comprises a shell,an air inlet and an air outlet are arranged at the two ends of the shell correspondingly, the shell is fixedly arranged on the lower surface of a top plate of the traffic hole, and the air inlet is adjacent to and faces an inlet of the traffic hole. Two partition plates I are arranged in the shell, the partition plates I are vertically arranged in a spaced manner and are perpendicular to the airflow flowing direction, and therefore the interior of the shell is divided into three chambers which sequentially comprise the first chamber, the second chamber and the third chamber in the airflow flowing direction, and the first chamber and the second chamber are a salt mist treatment chamber and a static pressure division chamber correspondingly. A partition plate II is horizontally arranged in the third chamber so as to divide the third chamber into an air supply static pressure chamber and an air curtain static pressure chamber which are parallel up and down. The air outlet is arranged at the position, corresponding to the air supply static pressure chamber, of the shell. According to the system, under the condition that the traffic hole is normally opened, fresh air subjected to salt mist treatment can be provided for offshore underground engineering, and natural invasion of outdoor salt containing air can be blocked.