A new method to calculate integral parameters for two-dimensional multi-electrode structures having symmetry axes or planes (conductivity, capacitance etc.) has been proposed. <...> The method is based on a simultaneous solution of algebraic equations for original and inverted systems (structures) connected between them according to the principle of rotatory invariance of two-dimensional potential and solenoidal fields. <...> Then unknown formulas obtained on the basis of this method for calculation of linear capacitance of a series of systems have been compiled in table showed in the Appendix. <...> The method makes it possible to extend the scope of application of Thompson—Lampard theorem on mutual partial capacitance per unit length in a system containing four cylindrical conducting plates with symmetry planes. <...> New solutions found on the basis of Thompson—Lampard theorem may be used to solve a wider range of problems in electric engineering. <...> The connection between exact solutions of symmetric multi-electrode systems and geometric parameters of regular polygons enables us to study the properties of similar systems without performing additional calculations. <...> The method may be used for calculation of not only linear capacitance but other integral parameters of two-dimensional physical systems under different conditions of symmetry and medium features distribution! <...>