Abstract: The elastoplastic seismic demand of structural systems, with stiffness, strength and combined eccentricity, subjected to pulse-like ground motions is investigated. Based on the newly-developed varying axial load-biaxial bending model, nonlinear time history analysis is conducted to study a single-storey RC frame subjected to eight ground motions, considering the pulse effect and eccentricity. The results of ductility, drift, torsion and rotation are discussed. The results show that eccentric system experiences higher elastoplastic demand under pulse-like cases compared with non-pulse-like cases. The stiffness eccentricity is insensitive to elastoplastic response, while the strength eccentricity has the most influences. The ductility in the weak side increases greatly with increasing strength eccentricity, and the maximum ductility is 3.09 times higher than that of symmetric structure. At the same time, the drift, torsion and rotation increase rapidly, and the rotation with eccentricity ratio of 0.2 is 6.4 times higher than that of 0.05. It is suggested that the strength eccentricity should be considered as a parameter in elastoplastic analysis of eccentric systems, and the velocity pulse-like effect should also be considered.