Abstract: In order to solve the problems that the combination mode of pattern elements in the decorative pattern design of grottoes was not flexible enough, the layout and adjustment of pictures in the design will be time-consuming and the overlapping of pattern primitives, a pattern generation method based on geometric similarity features is proposed. Firstly, it defined the pattern attributes and basic concepts. Secondly, Freeman chain code was used to describe the contour information of pattern primitives, and the longest common subsequence (LCS) was used to calculate the geometric similarity between pattern primitives. Based on the calculation results, the layout of pattern primitives was designed to complete the generation of subpatterns. Finally, the subpatterns were expanded according to the spatial distribution patterns detected and recognized. Experiments were carried out with decorative pattern primitives in Xiangtang Grottoes. The experimental results showed that the proposed method not only solves the problem of pattern primitive combination optimization, but also realizes the rapid generation and design of complex patterns. In addition, the matching time of the proposed method is 19.2 s, which is superior to 36.1 s of the artificial method.