In order to solve the problem of numerous and complicated contradictions in urban power grid planning, this article combined extenics theory with urban power grid planning theory. By analyzing the extensibility of contradictory problems in urban power grid planning, this paper preliminary acquired the solving process and framework of urban power grid planning contradictory problem by using Extenics theory. Moreover, taking a contradictory problem between high load density and power facilities as an example, this article using the extension rhombus thinking mode formally described the process of solving problems by extension model. Thus, it makes an attempt at enriching power system theory, as well as the application of extension engineering.