This research focuses on the critical energy release rate of fly ash concrete on the basis of the dual-G criterion. The fracture properties of fly ash concrete at different ages were tested by using three-point bending beams with different initial crack-depth ratios. The experiment results have indicated that the critical energy release rate grows with time before 7 days. While after 7 days, the critical energy release rate is almost unchanged. And the initial crack-depth ratio has no clear influence on the critical energy release rate. It can be concluded from this research that, for fly ash concrete, fracture parameter can be taken as the indexes in charactering the cracking resistance properties of concrete.