Evolution of Style Groups in the Flat Design Era from 2013 to 2020 ZHANG Ye, LI Xingxing, RAN Qilin Beiing Jiaotong University, Beiing 100044, China Abstraet: This paper aims to explore the evolution of Chinese mobile interface style groups in the flat design era, and describe the development and evolution mechanism of mainstream interface styles from 2013 to 2020. Starting from the analysis of the relationship among the three sources of flat style, the cause, characteristic, classifcation, evolution and interrelationship of more than 20 mainstream design styles in the flat design era are sorted out, and the demonstration is carried out along three ways of style evolution. Firstly, "almost flat era" has gone through three stages, including "selection adaptation period", "visual enrichment period" and "material expression period". Its new style mainly comes from breaking through the design rules of "flat surface ontology". Secondly, Based on existing style elements, which produces the two style groups, namely, the "early stage retro" and "expression technique imitation". Thirdly, new vintage style develops parallel with the flat style, which shows the trend of shifting from one to another. The development of above styles follows the underlying logic of the unity of opposites between flat and skeuomorphism design, which presents the evolutionary characteristics of "natural selection" and "survival of the fitst". The internal cause of style evolution is driven by social concept and aesthetic alienation, while the extemnal cause is related to the :| development of media. In the future, the popularity of synthetic styles based on fragmented "style memes" will be a major trend, and the public will become the creator of new styles.