To research fume-drainage time of tunnel after blasting, the formula of removal law of blasting fume in tunnel is deduced. Through calculating the grey correlation degree of influential factors of fume-drainage time, the ranking results of sensitive degree of main influential factors are: distance of entrance to tunnel face (0.827) > distance of duct to tunnel face(0.738) > air flow in duct(0.628) > initial volumetric concentration of CO in blasting fume(0.547). Blasting fume monitoring tests were conducted in tunnel to study the fume-drainage time when the distance of duct to tunnel face L_O are respectively 10, 15, 20, 25, 30 m and the distance of entrance to tunnel face L_P are respectively 40, 60, 80, 100, 120 m under the condition of forced ventilation. Research findings reveal that: fume-drainage time increases with the longer distance of entrance to tunnel face. The fitting result of the both is linear relation; fume-drainage time shows nonlinear rise with the addition of the distance of duct to tunnel face. The fitting result of fume-drainage coefficient c and L_O is linear relation, and calculation formulas of fume-drainage time in different working condition are concluded. Verification of equation is carried out in 5 tested similar tunnels. And relative errors are respectively 6.1%, 3.8%, 5.4%, 8.8%, 9.3%, which have remarkable accuracy and reliability