Abstract: Based on geometrical principle, an efficient and practical algorithm -fluctuation pursuit algorithm is presented in this paper. The fluctuation pursuit process takes into account the characteristics of randomicity and ergodicity. Relaxation factor is introduced into the pursuit process to control the calculation speed and precision. The simulations and demonstrations make it possible to visualize and comprehend the factual performances and properties of the algorithms, to prosecute the detailed and comprehensive parameters analysis. Two experimental examples validate that the algorithm possesses superb convenience and applicability, and provides an effective approach to the calculation of structural reliability index.