Abstract: Mesozoic red bed occurs and hydraulic projects spread widely in the Longquan area.Studies of the time effect of water-rock interaction of red bed are of engineering significance.After testing the softening coefficient of the samples of red rocks from four reservoirs,we obtained the changing regularity of softening coefficients after a long period of water-rock interaction.The results indicate that the softening coefficient of the red rocks reduce by 10% to 20% after 30 to 50 years of water-rock interaction,which is of important significance on the stable recheck of the reservoir-slope.