Using PCER (post-crack energy ratio) method, the influence of strength grade and curing age on flexural toughness of plain concrete were analyzed. Results show that along with the increase of strength grade and curing age, the flexural toughness of plain concrete decrease; and along with the increase of the K value used in the calculating equation, the flexural toughness of plain concrete decrease too. Meanwhile, the changing tendency of PCER value along with the K value manifests that when evaluating the flexural toughness of different quality concrete, the same K value should be used.
