Abstract: In order to optimize the designs and evaluate exactly the performances of PE/PE laminated composites, it is necessary to research the damage mechanisms of these materials, then to indicate the rules of the damage propagation, and to predict the effects on the various performances such as stiffness, strength and so on with the damage developing. A modified numerical model to simulate the mechanical behavior of PE/PE laminated composites was proposed based on the quasi-3-dimensional model concept. The damage propagation of three types of quasi-isotropic UHMWPE/HDPE laminated composites subjected to a tensile load was investigated by using the afore-mentioned model. The damage mechanism was analyzed and the strength was predicted for these materials. The experiments were done to verify the theoretical results. The results were consistent with those of the finite element numerical simulation. The validity of the modified numerical model is verified.