Aiming at nonlinear degradation data in occasion of Constant-Stress Accelerated Degradation Test (CSADT),a method for reliability assessment of nonlinear accelerated degradation based on Wiener process is put forward with consideration of individual performance degradation variation.The Wiener process is used to describe the degradation process of products.The time scale model is used to change nonlinear data into linear data.Drift coefficient of Wiener process is regarded as a random variable.The reliability model and accelerated degradation model are built up with consideration of individual variation.The Two-Step Maximum Likelihood Estimation method (TSMLE) is used to obtain the unknown parameters in the reliability model.An example is given to show the accuracy and superiority of the presented method.