Recently, piped irrigation systems have been getting more and more widely utilized. This paper aims to propose an integrated Non-domimated Sorting Genetic Algorithm II (NSGA II) and Multiply Criteria Decision Making (MCDM) method for finding the ultimately optimal design of piped irrigation networks when simultaneously considering minimum cost of pipes and maximum life span of pipes. The coupled method was applied on a real piped irrigation system consisting of 30 pipe segments. First, 11 Pareto optimal solutions were found by using NSGA II. Then, the optimal solution with the pipe cost of 11.5 ×109 VND and the life span of 43.6 years was ultimately selected based on Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) selection methods. The proposed coupled method could be applied to find optimal design for other piped irrigation systems.