Abstract: An analysis is made on the studying approaches of +θ/-θ interlaminar fracture toughness of composit-laminates.Under certain mechanical conditions the experimental techniques may becused to determine the "pure mechanical part" Gm of Gc.Combined with the "pure thermal part"GT evaluated numcrically,the value of Gc can be obtainced. A sufficiant condition is raised for DCB specimens.Under that condition,experiments and finite clement analysis are conducted for T300/648 and T300/QY8911 systems,which give the +θ/-θ interlaminer Gc for the range of θ=θ=0°～30°.The,The efffcts of large deformation are discussed and a new correction factor is propesed.A further discussicn is rnade on θ effectc and fractography.