In the paper an approximate algorithm for optimizing of distributed computing WAN network is proposed. Distributed computing systems become the common tools in different kind of business, science and even entertainment. In order to minimize processing time of data and utilize spare resources available on remote systems, many companies and institutions decide to build and maintain own wide area networks (WAN) for ensuring reliable and secure distributed processing of data. Design of WANs in concerned with solving different optimization problems, like routing assignment, capacities of channel selection, resource (i.e. servers, management centre) allocation. Due to peculiar structure of wide area networks and nature of protocols, proper optimization methods and algorithms should be constructed for WAN-based distributed computing systems. In the paper the model of the distributed environment, built on WAN infrastructure is presented. Then, the optimization problem for routing assignment, channel capacities assignment and grid management center (data repository) allocation is formulated. Finally, an approximate algorithm is presented for formulated problem. Proposed algorithm, observations and conclusions should effect in improving of distributed computing systems design.