In order to research the optimal parameters of dampers linking adjacent structures for seismic mitigation, two SDOF systems connected with visco-elastic damper (VED) are taken as research object and the primary structural vibration frequency ratio, connection stiffness and linking damping ratio as research parameters. Modified Kanai-Tajimi spectrum is selected to model the earthquake excitation. The peak distribution of power spectral density curves are analyzed, then the formulas of structural mean squared displacement (MSD) and research parameters is derived based on random vibration theory. Then the relationship of the adjacent structural seismic response versus the research parameters was presented. The optimal value of the linking visco-elastic damper damping ratio and stiffness ratio are investigated. Finally, the seismic responses of example structures with or without connecting dampers are contrastively analyzed. The dependence of response mitigation effective on research parameters is highlighted. The results indicate fine earthquake-reduction effectiveness of dampers connecting adjacent structures. It is also shows that optimal parameters of damper cannot reduce the seismic responses of the primary structures connected to the best extent simultaneously. The damper parameters should be determined according to the best seismic mitigation effectiveness of the primary, auxiliary structure or the combined structure system.