Abstract: In this paper, a "unified" ply optimization modle for in-plane laminates based or minimum strain energy criterion is built up, with the in-plane laminated element as structure modle whose main elastic axie coincids with its main orientattion of stress resultant, average strain energy density as the object function,the lamina fraction and fiber angle of lamina as design variables and materilas properties and total fraction of each kind of materials (for hybrid laminates) being given as the restrictions.