In this paper, a new approach for estimating the probability of failure is proposed. Due to high-computation cost of conventional sampling-based reliability analysis methods, this approach sequentially adds new samples in proper location. The method consists of two parts; space partiton part and additional sampling part. Space partition is conducted using Voronoi diagram, and new sampling location is determined by H cell strategy which discriminates the subspaces near the limit state function. The efficiency are compared with the results of other sampling-based reliability analysis methods, and they demonstrate the efficiency of the proposed method.