Abstract: Abstract: The ultra-long submarine tunnel has a special structure, so smoke exhaust and air supply are the key factors restricting the development of the ultra-long submarine tunnel. Based on Yanda Undersea tunnel, a new scheme of smoke exhaust and air supply without shaft in the sea is designed. It adopts centrifugal air compressor to pressurize fire smoke into seawater at high speed, and provides additional air supply through compressed air. FDS was used to simulate 56 groups of working conditions with different smoke exhaust volume and air supplement volume. By analyzing smoke layer thickness, smoke spread length, smoke exhaust efficiency and evacuation environment, the optimal smoke exhaust air supplement scheme was found. The results show that when the exhaust volume is 140-180 m3/s, and the air supplement volume is 190-210 m3/s, respectively, accounting for 50% and 70% of the exhaust volume, the system has the best exhaust effect. Among them, the smoke exhaust system of 180 m3/s, 50% air supplement volume and 200 m3/s, 70% air supplement volume has the best smoke exhaust effect, and the latter is better than the former. In practical engineering application, it can be considered that the design smoke exhaust volume is 200 m3/s and air supply volume is 140 m3/s.

Key words: Key words: ultra-long submarine tunnel, exhaust system without shaft, FDS simulation, smoke exhaust volume, air supplementary volume