Abstract: Fire extinguishing system in underground passage is strictly required by its particularity. Fine water mist, as a kind of modern fire extinguishing technology, is widely used in fire fighting in underground passage. Effectiveness of fire suppression by fine water mist in underground passage at a commercial district in Chengdu is validated by FDS simulation. Combination of fine water mist fire extinguishing technology with mechanical smoke extraction can achieve the best fire suppression effect.