Butted cylindrical shell structure is widely used in aerospace, shipbuilding, civil engineering and mechanical engineering. Modal analysis is an important research direction to study its structural characteristics. This study briefly introduces the modal analysis technology and the basic principle of the polyreference least-squares complex frequency-domain method (PolyMAX), and the finite element modal analysis and experimental modal analysis of butted cylindrical shell structures are carried out. In the process of experimental modal analysis, the experimental realization of the free boundary and the correctness of the analysis results are discussed, and the analysis results are compared with the finite element modal analysis results. The results show that while the butted cylindrical shell structure has the general vibration characteristics of the cylindrical shell structure, the asymmetric vibration with the flange as the boundary occurs due to the existence of the docking form.