Abstract: Two dynamical analysis methods are discussed in this paper for an accidental eccentricity during the computation of horizontal seismic responses of tall buildings. They are the modal response spectrum analysis method and the equivalent torque method. The results of two groups of structures demonstrated graphically in terms of the ratio of uncoupled lateral and torsional periods show that the equivalent method has a good precision when the ratio of periods is larger than 1.8. However, it may underestimate member forces if the ratio is close to 1.0. Therefore, a modified approach should be involved in applications.