In order to improve the field reliability of products and reduce the total cost of burnin procedure and warranty, an optimization method of accelerated burn-in time for products with infant mortalities within the reliability and cost constrains was developed on the basis of utility function. Considering the uncertainties with respect to the lifetime distribution parameters of the product, the prior distributions of these parameters were derived by using the bootstrap method, and then the joint utility function combining field reliability with cost was constructed through simulation technique. Choosing the maximum of joint utility as objective, the optimal accelerated burn-in time model was established, and the optimal burn-in duration was derived. The application of the above method was illustrated explicitly by a numerical example in which a product with log-normal distribution was burned in under elevated temperature condition, and the parameters′ sensitivity analysis was also conducted. The results show that the proposed method not only can shorten the burnin duration, but also can meet the requirements for cost and reliability simultaneously to the utmost.