The double-decked tunnel is limited by the size of the shield tunneling and the surrounding environmental conditions, and its ventilation and smoke exhaust conditions are not good. How to ensure the ventilation and fire safety is a problem that must be solved to ensure the safety of the project operation.This paper carries out relevant research through the longest double-decked tunnel project —— Shanghai Beiheng Passageway, which has been opened to traffic. The project using the key smoke exhaust scheme under blocking conditions, especially the lower smoke exhaust duct is restricted by the structural space size, and the setting conditions are very cramped.In order to verify the reliability of the key smoke exhaust system, through the calculation, analysis and comparison of multiple working conditions, determined the relevant design parameters of the key smoke exhaust, and verified the smoke exhaust effect, to ensure the safety of personnel evacuation under the tunnel fire conditions.