Abstract: Based on a previous paper the theoretical formula with the weighted factor and oriented angles of different kinds of fibers as optimum parameters,for hybrid or thotropic cylindrical shells is given. The usable conditions are discussed. A discriminant,which enablas one to identify whether the optimun parameters are extreme points,is proposed for the hybrid fiber cylindrical shells under the external pressure. The examples in this paper show that the formula can be used not only to determine the optimum paremeters for hybrid fiber cylindrical shell,but also to find out the optimum fiber content and the ply orintations of fiber for fiber reinforced homogenous cylindrical shells.