This paper proposes a new life prediction method using time series and grey theory to predict product life based on Constant-Stress Accelerated Degradation Testing (CSADT) data. CSADT degradation data is modeled using time series method and predicted using grey theory. A four electric stress levels CSADT of miniature bulb is conducted to verify the proposed method. A comparison among life prediction by the proposed method, traditional methods, and real life of miniature bulb is processed. The result shows that life prediction by the proposed method is more accurate than traditional methods.