Abstract: Damping is an important parameter in governing structural dynamic responses. Traditionally, the Rayleigh damping model, constructed for the convenience of computational decoupling, is used in structure dynamic analysis, but it has no clear physical meaning. Based on complex damping theory, the 3D FEM dynamic program is developed using newmark-b integration method, which can be used for solving Rayleigh damping model and complex damping model. The seismic time-history response and loss factor of a steel frame structure are obtained. Furtherly, this paper discusses the effects of peak acceleration and time integration size on time-history response and loss factor. With complex damping model, the structural response is 50%-100% larger than that with Rayleigh damping model under El-Centro earthquake excitation. It is also found 1) the loss factor increases with the stress or displacement development, 2) using complex damping model, the precision of structure dynamic response is affected by time integration size, inappropriate time integration size may result in the divergence of results.