A set of full scale contrast tests, with different relative positions of air supply opening and smoke exhaust opening, were conducted in an 88 m long underground corridor to study the effect of position of air supply opening on the efficiency of smoke extraction in a long channel. Results showed that the rule for designing the relative positions of air supply openings and smoke exhaust openings or operating them in a long channel should be “Smoke exhaust near the fire with air supply far away from the fire”.