Abstract: Stiffness reduction models of fiber reinforced polymer composite laminates published in recent two decades were reviewed in the present paper. According to their methodologies, these models were classified as theoretical models, semi-empirical models and empirical models. The theoretical models are those entirely based on the mechanical analysis and include mainly shear-lag models, fracture models, elasticity mechanics models and etc. Theoretical models establish the relationships between micro damage mechanism and macro stiffness reduction of the laminates. The empirical models were established based on experimental data, so an empirical model is often simple and easy to understand and to apply. The semi-empirical models are those between the theoretical and the empirical ones.