Abstract: The elastic-plastic stability problems of cylindrical shell under internal pressure and axial compression are studied on the basis of the theory of nonlinear elastoplastic stability.The principle of effects of different proportional load paths initial imperfect and plastic deformation on elastic-plastic sta bility is obtained. Results show that critical wrinkling axial compression stresses will increase at the beginning stage but the stresses will reduce when the internal pressure reachesa certain value. And the critical wrinkling axial compression stresses will descend with the increment of imperfect factors.The study shows the following as well for the same imperfect factor the critical wrinkling axial compression stresses will increase with the increment of the proportional load parameter D when D value less than 1.0 but the values will fall down when D greater than 1.0. The ideal load path is the proportional load parameter equal to 1.0. The investigations enrich the theoretical background for internal high pressure forming technology.

Key words: Cylindrical shell Elastoplastic stability, Proportional load Imperfect factor