Abstract: Based on the explicit expressions of dynamic responses, a dime-domain explicit formulation random simulation method was developed to remarkably improve the efficiency of a dynamic reliability analysis by reducing single sample calculation time. However, for small failure probability events, the computational cost is still quite considerable because of the requirement of a large number of samples. To overcome above difficulty, a basic idea of subset simulation that expressing a small failure probability as a product of lager conditional probabilities is introduced to the dime-domain explicit formulation random simulation method to further lower the sample number. Among them, the conditional probabilities are obtained by the dime-domain explicit formulation random simulation method, and the samples required for obtaining the conditional probabilities are generated by Metropolis-Hastings algorithm. Numerical results show that the improved method has a higher computational efficiency and especially applicable for the dynamic reliability problems of small failure probability and for multi-degree-of-freedom structures.