Lingzhao Xuan in the Forbidden City is one of the oldest steel-masonry composite structures in China. The building has very important historical, artistic and scientific value. In order to evaluate the structural safety of the building under earthquake conditions, we set up a three-dimensional finite element model to analyze its dynamic properties and earthquake response in order to obtain natural frequencies, modal modes, the earthquake displacement response and the earthquake stress response. The results show that the structure of Lingzhao Xuan is very symmetric and its torsional rigidity is large, which is better for the seismic behavior of this building. Under conditions of 8-degree frequently occurring earthquake, 8-degree fortification earthquake or 8-degree rarely occurring earthquake, the maximum displacement and the maximum story drift of the building can meet the requirements of the present codes, and the maximum compressive stress of this building is lower than that of the masonry, so the building has no fracture failure. Under conditions of 8-degree frequently occurring earthquake or 8-degree fortification earthquake, the maximum tensile stress of this building is lower than that of the masonry, so the building has no cracking failure. However, under conditions of 8-degree rarely occurring earthquake, the maximum tensile stress of some parts is larger than that of the masonry, and these position will have cracking failure. Finally, the seismic strengthening strategy of this building is presented based on the results of the dynamic properties and seismic behavior analysis.