Abstract: This paper provides afailure model of the crack tip from the fact that the concrete presents visible viscoelastic under the long-time and continuous action of load,and according to the date given by modern examing and observing techniques for tensined concrete samples having a notch.The general laws have thus been researched for the early stage propagation and delayed instability of cracked conerete by the action of long-time and sustained load.Therefor,it is of practicle signicance to predict the service life of delayed crack instability for the concrete strctures during long period operation.