The symmetries of four kinds of resistance networks are analyzed, and the simplified equivalentcircuits are drawn according to the symmetries, and the series-parallel relationship between each resistor isdefined.Based on the basie law of series parallel resistanee, the equivalent resistanee values between networknodes are caleulated, On this basis, the equivalent resistanee between the other asymmetrical two points iscalculated by using the electric current superposition method.The extension shows how to solve some physicsproblems without symmetry by constructing symmetry. This method not only enhances the accuracy andefficieney of calculations but also provides a new approach for solving complex physical problems.