The modeling methods for Room Temperature Vulcanization(RTV) adhesive in a reflective mirror structure were investigated. The modelling methods of node-connection(ignoring RTV adhesive)),isotropy(three elements and one element) and anisotropy materials were introduced, respectively. The Finite Element Analysis(FEA) models of lens sets were established by three methods and the simulated mode was analyzed. Furthermore, the mode test equipment was setup and the mode parameters were tested for lens sets. The results show that the error of the first-order free mode frequency between the modeling method of anisotropy and the test method is only 0.3%, and the errors obtained from the three modeling methods of the isotropy of three elements, isotropy of one element and node connecting by are 1.8％, 1.2％ and 13.9%,respectively. From the anlysis and test, it is concluded that the RTV adhesive can not be ignored in FEA and the modeling method of isotropy of one element is a best choice to reduce number of models and to satisfy engineering requirements.