Abstract: For a closed-loop logistics, it is important to design a network such that it can operate effectively and at the same time recycling rate of waste materials can be increased. It is assumed that hybrid distribution and collection center is adopted for the system. A multi-product, multi-period, and multi-stage closed-loop logistics network location and transportation model is presented for this purpose. It is a multi-objective optimization model for minimizing both economic cost and time. In order to solve this problem, an evolutionary algorithm with a priority-based encoding method is proposed，leading to the Pareto front. The proposed method is compared with the constraint method. Results show that, by the proposed method, the average error is less than 5%. In other words, the proposed evolutionary algorithm describes Pareto front well, and its results are correct and reasonable.

Key words: closed-loop logistics, multi-objective optimization, evolutionary algorithm