Abstract: Fracture is the main failure form of marine structures due to the action of ocean waves. It is necessary to monitor the initiation and extension of the crack timely and accurately, and the SIF (Stress Intensity Factor) is an important indicator for judging the propagation of cracks. Based on the existing research, this study combines the calculation method for SIF based on single strain gauge (SSG) and maximum crack opening displacement (CMOD) and, proposes a method based on Kalman filter (KF). Numerical simulation and experimental verifications of this method have been carried out. The results show that the method can be used for a variety of configurations of pre-cracked specimens. And compared with the SSG-based and CMOD-based methods, the KF-based method can obtain more accurate results, the relative errors (RE) is not more than 1.2%.