Dynamic reliability is defined as the probability that an engineered system successfully performs the predefined functionality over a certain period of time considering timevariant operation condition and component deterioration. In practice, it is still a major challenge to conduce dynamic reliability analysis due to the prohibitively high computational costs. In this study, a confidence-based meta-modeling approach is proposed for efficient sensitivity-free dynamic reliability analysis, referred to as double-loop adaptive sampling (DLAS). In DLAS a Gaussian process (GP) model is constructed to approximate extreme system responses over time, so that Monte Carlo simulation (MCS) can be employed directly to estimate dynamic reliability. A qualitative confidence measure is proposed to evaluate the accuracy of dynamic reliability estimation while using the MCS approach based on developed GP models. To improve the confidence, a double-loop adaptive sampling scheme is developed to efficiently update the GP model in a sequential manner, by considering system input variables and time concurrently in double sampling loops. The model updating process can be terminated once the user defined confidence target is satisfied. The DLAS approach does not require computationally expensive sensitivity analysis, thus substantially improves the efficiency of dynamic reliability assessment. Two case studies are used to demonstrate the effectiveness of DLAS for dynamic reliability analysis.