A modified Shear-lag model and variational approach were used to predict the effect of the crack density on the stiffness degradation for composite laminates with different fiber orientation angle of the cracked layers. Good agreement is obtained by comparing the prediction models and experimental data published by Katerelos. Furthermore the cracked off-axis composite laminate is submitted to hygrothermal conditions. The material properties of the composite are affected by the variation of temperature and moisture, they are based on a micromechanical model of laminates. The transient and non-uniform moisture concentration distribution give rise to the transient elastic moduli of the off-axis cracked composite laminates. The modified shear lag analysis has been extended to study the stiffness properties degradation of high-temperature polymer composite material at both, room temperature and high temperature. The obtained results represent well the dependence of the stiffness degradation on the cracks density, fibre orientation angle of the inner layers and operating temperature.