Abstract: In this paper, the precision method for optimizing the reliability of a redundant control system with single or multiple constraints have been investigated. This method is presented in an easy way. Starting from the physical concept for the least cost and the most benefit in engineering design, we obtain two criteria and a basic principle for optimizing the reliability of a control system with single constraint. For a multiple-constraint problem we can find out only one active constraint in general or sometimes a few active constraints. All the other constraints are non-active and can be discarded without any trouble. Once the ideal solution has been obtained, this solution should be rounded to integral numbers.