Abstract: An experimental program which includes lots of unidirectional laminas is conducted using T300/BMP-316 material for researching the static and fatigue behavior of the unidirectional ply to set up the expressions of the residual strength degradation and the residual stiffness degradation of a unidirectional ply in the longitudinal, transverse and in-plane shear directions. The factor of nonlinear shear stress-strain behavior is acquired. The expression of shear stiffness in the 1-2 planes during fatigue loading is given. Dye-enhanced X-radiography was used to nondestructively check the specimens. The damage mechanisms are also analyzed. The results obtained from the experiments show that considering the nonlinear shear stress-strain behavior of a unidirectional ply is important in the analysis of stresses for composite laminates.