The mathematical concept of green design method is proposed based on the relation between energy and life cycle, including domain redefinition, geometric probability, failure rate and reliability expression. The product design is carried with failure distributions and design steps, including exponential, normal and Weibull. The parameters are redefined and design steps and flowchart are specified. This proposed method is to ensure reliability and resource utilization for electrical products, and compares with traditional reliability assessment method. For traditional design method, the higher reliability requires more resource reserves and longer life cycle in material supply chain. Products are passively eliminated due to technical progress and resource utilization is lower during life cycle. green design steps and reliability test are simulated with Monte Carlo method, to demonstrate the correctness of green design method. This study involves higher reliability and considers reasonable life with more resource utilization than traditional design method.