In present work has been made investigation of delamination between skin of shell and flanges of a stiffener by experimental testing and numerical analysis. Energy release rate has been evaluated from experimental testing under Mode I and Mode II loading conditions. The investigation has been made with aim to find the parameters for prediction a crack growing under different kind of stiffened shell loading. The numerical analysis of the structure with has been made using computer code ANSYS/LS-DYNA for explicit analysis of delamination. The energy release rate has been calculated in the damaged zones using Virtual Crack Closure Integral method [2] and so-called Tehnique-B. A crack front of delamination has been investigated since this one has considerable influence on energy release rate in the composites. A crack front isn’t a straight line and depends as from stiffness of the web flanges, as from directions of layers stacking at the delaminated surfaces.