Many studies have shown that the linear elastic fracture mechanics (LEFM) method based on the stress intensity factor range (ΔK) has limitations that cannot be ignored. Due to neglecting the influence of plastic deformation near the crack tip, LEFM shows apparent deviations in evaluating the fracture behaviour. Therefore, in this study, the crack tip opening displacement range (ΔCTOD) is chosen as an alternative to ΔK and based on the elastic–plastic fracture mechanics (EPFM) to develop a new fracture behaviour assessment approach for marine structures. Firstly, a ΔCTOD model based on the HRR (Hutchinson, Rice, and Rosengren) solution is proposed considering the crack closure effect. Secondly, a series of compact tension (CT) specimen crack growth experiments under constant amplitude loading is carried out. According to the experimental results, the prediction accuracy of the HRR model and traditional Irwin and Dugdale models is compared and analysed. The rationality of ΔCTOD as an alternative to ΔK is verified. The results show that ΔCTOD can describe the crack propagation behaviour well. The proposed HRR model shows better accuracy and a more comprehensive application range than the traditional models, which has a guiding significance for studying fracture behaviour for marine structural applications.