Abstract: Subset simulation with splitting is an efficient method for small failure probability estimations of structures subjected to random excitation. A nested sequence of failure regions is assumed and offspring trajectories are derived through splitting. For a response conditioning method, a linear response can be used to estimate a nonlinear response, or the response of a single degree-of-freedom structure can be used to estimate the response of a multi-degree-of-freedom structure. A modified response conditioning method is proposed by combining subset simulation with splitting and a response conditioning method. The failure probability formula is developed using the theorem of total probability for the modified method. The non-overlapping bins of a response conditioning method are related to the sets of subset simulation with splitting. Then the failure probability can be expressed through subset simulation with splitting. The computational times of nonlinear structure responses or multi-degree-of-freedom structure responses are decreased obviously. A three DOF linear structure and a single DOF nonlinear structure subjected to random excitations are calculated using the modified response conditioning method. The computational results show that the proposed method is an effective way for dynamic reliability estimations, and is efficient for small failure probability calculations.