Abstract: The steel-concrete-steel(SCS) sandwich composite structure is an important structural design for an immersed tube tunnel.Studies on the heat transfer in this composite structure under different fire scenarios are of important significance for the fire risk evaluation of a sandwich-structured immersed tube tunnel during the operation period.Taking the types of vehicles involved in the fire in the tunnel as classification standard, a total of 12 tunnel fire scenarios are designed, including different vehicles such as cars, light vehicles, buses, and heavy trucks.A three-dimensional(3D) finite element numerical simulation model is established for the SCS sandwich-structured immersed tunnel to simulate the heat transfer in the structure with or without fireboard in the fire scenarios.The results show that in the SCS structure, when tunnel fire of burning buses or other more serious fires occur without the fireproof panel, the temperature of concrete will reach the limitation for fire safety set by the Code of Practice for Fire Safety in Buildings, while when the fireproof panels are equipped, the temperature field of the structure is within safe limits in all fire conditions.The results can provide reference of design of SCS immersed tunnels.