A basic formulation for evaluating the failure path of composite laminates is presented. The proposed formulation is based on an in-plane failure criteria and first-order reliability method (FORM). The sequential failure path of each layer of composite laminates is simulated by means of modulus degradation and safety indices under the off-axial load conditions. Numerical analyses of graphite epoxy composite laminates are performed corresponding to various lamination configurations with symmetric lamination angles subjected to off-axial in-plane strain conditions. From the simulation analysis, a typical failure path is evaluated corresponding to an in-plane strain vector. The mechanical behaviors such as decreasing modulus and increasing in-plane strain are also simulated in correspondence with each stage of sequential ply failure. The proposed simulator enables one to search the effective failure path in order to evaluate the last ply failure probability of laminates.