A structure consisted of shallow shell with stiffners is usually analyzed by the method simulated to folded plates or three dimensional frameworks in actual ship-hull-design. These methods of analysis cannot take account of the effect of curvature of shell strictly. One of universal and powerful method for this subject is finite element method. However, finite element method has inconvenience such that extensive calculation due to a large number of freedom is usually needed and in addition increasing number of freedom does not necessarily assure to increase accuracy except by a few particular cases. This paper presents an analytical method on strength of shallow shell with stiffners by improved finite strip method proposed by author to lighten the volume of calculation. Displacement functions of strip elements are employed the approximate function obtained by Kantorovich method. Those give exact solutions for some special cases and which satisfy the equilibrium equation of shallow shell or very close ones to them for other cases and this procedure is effective to make decrease of discretization errors. Some examples are shown for the cases of analyzing bending of shallow shell without and with stiffners of which all edges simply supported. The results prove that this method is one of effective means for analyzing of shell structure.