Abstract: In the research of the limit strength of laminates under combined loading,a new tensorial strength criterion and a combined strength theory of laminates based on the basic strength and optimal experimental strength of laminates are proposed.With a newly developed Degradated Ply Stiffness Theory and "Uniform Degradated Stiffness Coefficient" from experiments,the last ply failure (LPF) is predicted.Moreover,the Degradated Tensorial Strength Criterion of laminates is established.The criterion has the advantages of using lamina property,with the help of uniform degradated stiffness coefficients,to predict the ultimate loading capacity of any laminates under multiaxial loadings.It shows that the correlation between the experimental results of a series of typical laminates,in both plates and tubes,under multiaxial loading,and the theoretical predictions is reasonable.The presented criteria and the engineering methods of strength design are believed to be valuable and to be of practical significance in structural design.