The work proposes a nonlinear combination, two-parameter damage model of maximum deformation and hysteretic energy dissipation. Comparing the performance of the proposed model with that of existing damage models reveals that the proposed model can accurately reflect the earthquake damage mechanism. For comparison, the structural damage curves and seismic fragility curves of two single-parameter models (deformation and energy) and two two-parameter models (Niuditao model and the proposed model) are drawn in accordance with the incremental dynamic analysis results of an eight-story RC frame structure under the input of 50 seismic waves. Results show that structural collapse performance will be overestimated when the interstory drift angle is used as the sole structural damage index, whereas the exceedance probability of structural damage will be underrated if energy dissipation is used as the sole structural damage index. The proposed model can well balance the influence of maximum deformation and cumulative damage on structural damage.