Abstract: A large number of structural planes with very discrete distribution are usually developed in complicated structural rock slopes. These slopes' failure mode is mainly controlled by spatial distribution of structural planes and combination relationship between structural planes and slope surface. The general analysis idea is : 1 collecting occurrence data of rock mass structural plane; 2 analyzing dominant structural plane direction; 3 judging deformation and failure mode of slope. However, when the number of structural planes is large and the distribution is very discrete, the commonly obtained statistical dominant structural planes are likely to not fully represent the impact of all structural planes on slope failure mode. Firstly, a set of structural plane occurrence data was generated whose center was 270°∠50°,the slope surfaces in five different occurrences of 270°∠70°, 270°∠50°, 270°∠20°, 0°∠30°, 90°∠45°were assumed. After failure mode analysis, it was pointed out that there were obvious shortcomings in judging the slope failure mode according to the combination relationship between the dominant structural planes and the slope surface based on the traditional dominant grouping schemes. Then the slope of Yangjiagou quarry in Jingyue District of Changchun City was taken as an example, the geometric parameters of the slope rock mass structural plane were obtained by using the UAV three-dimensional real modeling technology. The structural planes were divided into from 2 to 10 groups by using firefly optimization method, and the differences of the dominant grouping schemes corresponding to different grouping numbers were compared. The stereographic projections of the dominant structural planes in two groups and the stereographic projections of the dominant structural planes in nine groups were plotted respectively. The slope failure modes considering two different dominant grouping schemes were compared. The results showed that when the structural planes were divided into two groups, the slope was judged to be basically stable. When structural planes were divided into nine groups, the slope was judged to slide along structural plane. In addition, when structural planes were divided into nine groups, the occurrence distribution within each group was more concentrated, the nine dominant structural planes could preferably represent the control effect of all structural planes on the slope failure mode, and the results were more in line with the site preliminary understanding. The following conclusions are drawn. Different dominant grouping schemes of structural planes may lead to different slope failure modes. The grouping scheme should fully consider the effect of structural planes on the slope failure, thus the conclusion which is consistent with the actual can be obtained.