For the flow Steiner tree problem on a transport network, a two-level composite evolutionary algorithm was developed. At the upper level a tree topology is searched; at the low level optimal Steiner points’ coordinates are searched for the three with a given topology. In this paper for solving the latter problem, a real-coded evolutionary algorithm is suggested. The algorithm uses an ontogenesis model and a special maturation operator. The operator is based on a random modification of the coordinate-wise-decent method adapted for the flow problem.