Impermeability of tunnel structural material after exposure to high temperature determines residual service life and security. The present study explores impermeability deterioration and water absorption change (expressed as w(T, t)) of tunnel structural material after exposure to 200 ℃,300 ℃, 400 ℃,500 ℃, and 600 ℃ respectively. Structural cementitious material was devised according to the requirements of segment used in Yangtze River tunnel of Wuhan which has been in constructing. Effect of high temperature on impermeability is evaluated by impermeability deterioration factor (abbr. IDF) and w(T, t).Testing results indicate that impermeability of concrete decreases with the increase of temperature up to 600 ℃, and serious impermeability deterioration occurs at temperature above 300 ℃. Furthermore,concrete with higher impermeability is more sensitive to high temperature above 400 ℃.