The sophisticated ships such as LNG or LPG carriers has been playing an important role in the clean energy campaign. To meet the strict qualifications against the crack failure and to make structural design much more rational and compatible with the actual defects in these ships, the so-called fracture mechanics analysis is appropriate and applicable. The authors have tried to carry out the fracture mechanics analysis on the member of the ship hull structures. As an example taking the panel with the stiffener, the crack tip K -value etc. has been calculated and the crack propagation life is deduced by adopting the proper simplifications and expedients. And to make the analysis simple and easy to execute for the similar structural members, the approximate calculation has been formulated. And the usefulness of the present approximation has confirmed by following the test results of the fatigue crack propagation rates and the stress distribution in the cracked stiffener.