Railway network is the large-scale logistics network. Logistics management for the large-scale railway network is a very complicated problem. If the rail system owns by the one owner or it is managed by the single unified operator, then there exists the problem of network design and decomposition into some local subnets or territorial zones. Decomposition needs to be performed for operations optimization. Railway territorial zones can be managed and serviced by the separate management centers. This paper examines the decomposition design problem for the large-scale railway network. A network with one input and multiple outputs is considered. Decomposition is performed along the main lines. Optimality criterion for decomposition problem is presented. The problem of optimal points finding for railway network decomposition along each main line is solved analytically for the given criteria.