<p>The sampling method is an important numerical technique for solving reliability problems in engineering systems. However, the evaluation of the failure probability using classical sampling methods is time-consuming for complex engineering structure. To address this issue, this paper proposes a gradient optimization assisted bubble sampling method (GOBSM) to reduce the computational costs, which enhances the coverage range of bubbles, thereby improving the computational efficiency without sacrificing the accuracy. Furthermore, the bubble gradient iterative algorithm is developed to efficiently construct bubbles. Eight complex numerical examples are tested for assessing the failure probability, and the results demonstrate the performance of GOBSM.</p>