Abstract: The variable elastic modulus method is presented in this paper, with which the complex structure can be simplified for the purpose of calculation. Combined with some numerical methods, such as boundary element method and finite element method, the variable elastic modulus method can be used to solve practical engineering problems. Examples are given, the application of Somigliana Formula to boundless domains is discussed, and the important conclusion has been reached that if no force is exerted on any infinitely large object, then no rigid displacement will occur.