<p>Based on the adjoint symplectic subspace iteration method and the sector model, an efficient method is proposed in this study for modal analysis of multistage cyclic structures with gyroscopic effect. Different from the adjoint symplectic subspace iteration method based on the entire multistage model, the method proposed in this paper only uses the matrices of sector models of multistage cyclic structures, thereby reducing the demand on the computer resources. Due to the cyclic symmetry of each stage, the computational cost of solving the linear algebraic equation system for each disk can be significantly reduced by using group theory and the properties of block circulant matrices. The proposed method is equivalent in accuracy to the adjoint symplectic subspace iteration method based on the full model matrices; however, it exhibits superior computational efficiency. The computational advantages of the proposed method are particularly evident for multistage systems with a high number of stages and sectors. The accuracy and efficiency of the proposed method are verified through three numerical examples.</p>