A simplified model for seismic analysis of a 1 000 MW tower type lignite boiler steel structure was studied, in which the mass of boiler is added to main steel structure replacing its seismic action. The seismic behavior differences among the simplified model and two models with boiler are studied. One of the two models with boiler used steel bars to inhibit sway of boiler. All of the models remain elastic under small earthquake actions, and the stress responses are the largest in simplified model. Under strong earthquake actions, some concentrically compression steel braces are buckling with plastic deformation and some beams have plastic deformations while eccentrically steel braces in the main steel structures and steel columns remains elastic. Some members near the steel bars develop plastic deformations due to the increased loads applied by the bars, which should be considered in design. Under both small and strong earthquake actions, inter-story deformations of the main structures are much smaller than the design code limits. Both lateral deformations and inter-story deformations of the main structures in the simplified model are the largest.