Setting up the complex electromagnetic environment is a basic part of training conditions construction. It is important to evaluate the similarity between training electromagnetic environment and required environment. In view of the unclear index system for electromagnetic environment construction and the incomplete similarity evaluation， the similarity evaluation index system is constructed by Euclidean distance. By the way， the similarity characterizations of basic arguments and mode arguments are analyzed based on the basic principles of similarity theory and electromagnetic environment constructing practice. According to the electromagnetic environment properties， the similarity degrees are calculated in multiple dimensions such as threatening electromagnetic environment， objective electromagnetic environment and background electromagnetic environment， the environment mentioned above are aggregated to obtain the expression for evaluating the similarity of electromagnetic environment. The methods can be used to evaluating electromagnetic environment constructing effect， and provide reference to optimize the electromagnetic environment construction.