The softening curves of four groups specimens with different sizes were obtained by inverse analysis based on the fictitious crack model(FCM)and the P-CMOD curve achieved by a three-point bending notched beam (TPB) test. According to the softening curves obtained by inverse analysis, size effect of softening curves was investigated,which shows both the tail of calculated softening curve, namely the maximum crack width wcand fracture energy GFhave an increasing trend with the increase of the specimen size, but no longer to increase when the specimen size attains to a certain level.