In work the system approach to formation of the urban power supply system is given. The hierarchical structure of the construction, voltage levels and load densities is considered. The mathematical and geometrical modeling of service areas for transformer substations of different voltage is fulfilled. Determination of perspective loads of transformer substations is given. The method of graphic placement of transformer substations in the city territory for new substations at existing structure of networks is offered. The calculation program Microsoft EXCEL and the graphic program AutoCad are used for realization of method. The method allows finding a rational decision for the development of urban power supply system on the beginning design stages in conditions of the information uncertainty.