In case of tunnel fire at congest traffic, central smoke extraction by controlling the longitudinal flow velocity can confine and extract the fire-induced smoke in a short time, and retain the natural stratification as well as possible for obvious reason of safety. With respect to three vents located on both sides of the fire in an asymmetrical arrangement, a series of experimental tests are carried out in a 1/14 reduced scale model tunnel. For the experimental simulations, fire induced smoke is simulated by a heated air release using the model proposed by Mégret et al. Detailed temperature distributions in the tunnel have been carried out. According to the test results, it is difficult to give consideration to the smoke control both upstream and downstream the fire. At critical ventilation, until the exhaust rate Ge is more than 519m3/s, air temperature in the respiratory region can decrease to 322K for people survival.