Abstract: Discussion was made on the optimum design method for MTLD system to control the seismic responses of tall steel structures. The equations of motion of the structure-MTLD system were derived. Based on the dynamic magnification factor (DMF) of the structure-MTLD system, numerical analysis was conducted to study the relations among the parameters for MTLD system, and the optimum parameters for MTLD system were obtained.The design steps for MTLD system and the concrete design method for structure-MTLD system to withstand earthquake were introduced. Eventually, a 30-storey steel structure-MTLD system was analyzed in time domain under seismic excitation