Stress intensity factor（ SIF） for cracked engineering structures under different loading is one of the core issues of fracture analysis. A slender fin-shaped shell possesses both shell and beam characteristics,in the cross-section of which some typical periodic cracks,such as the periodic cracks on fins and circumferential cracks,may arise usually. There will be different singular stress fields next to crack tips for a cracked fin-shaped shell under bending. Based on the conservation law and the elementary mechanics,a technique to determine SIFs has been proposed in this article,which is simple and easy to understand.The SIFs calculated by using of the present method agree well with the FEM results.