Characteristic mode (CM) theory can describe the radiation and scattering properties of arbitrary objects based solely on their geometric shape and material properties. It satisfies the requirement of solution accuracy and has a clear physical concept, which has guiding significance for electromagnetic structural analysis. However, traditional characteristic mode methods are difficult to achieve fast solutions for large-scale electromagnetic scattering problems. To address this issue, this paper mainly studies the combination of low-rank fast algorithms and characteristic mode methods, and incorporates the adaptive cross approximation (ACA) algorithm into the solution of characteristic mode problems. An example of using characteristic modes to analyze the radar cross section (RCS) and mode characteristic values of a missile are given in this paper. The implicit Arnoldi iteration algorithm is used to solve the eigenvalue equation, and the ACA algorithm is used to accelerate the solution process and reduce memory consumption. This method can be extended to antenna design and electromagnetic structural analysis.