A simple stiffness degradation method was proposed based on the model of individual unidirectional ply within the laminated composite. The model simplified Zinoviev’s theory of individual unidirectional ply under transverse loading and shear loading. 2D Hashin criterion was employed to predict the failure of individual ply in laminates. With the help of increment method, a program was complied to analysis the failure behavior of composite laminates. With this program, the failure of composite laminates of various layup and materials were predicted. The results demonstrated that, on the premise of maintaining the high accuracy of Zinoviev’s theory, the proposed model simplified the calculation process and could be easily applied to further study.