Under the background of mobile Internet era, cosmetics industry has ushered in new adjustments and changes in brand strategy and marketing methods. This paper takes Perfect Diary as the research object, from the perspective of brand strategy, analyzes the market data and brand strategy of Perfect Diary by combining quantitative and qualitative research methods, and explores the diversified marketing mode of this brand. In brand strategy, Perfect Diary chooses to capture those unsaturated category markets and looks for a breakthrough from the less competitive blue ocean market. Based on such market selection, Perfect Diary focuses more on online marketing with lower cost and greater influence. It makes full use of Internet social media and other channels for product and brand promotion. Through the research on the purchasing behavior and purchasing psychology of the target consumer groups, Perfect Diary has gained a large number of consumers’ favor by designing diversified marketing and a set of perfect customer service system. The development experience of this brand provides an effective way for cosmetics brands to choose an appropriate market focus, improve brand awareness by using network traffic, and cultivate loyal consumer groups. From the theoretical point of view, this paper expounds on the importance of the blue ocean market and the advantages of using diversified marketing to maintain consumer groups under the background of the Internet. From the practical point of view, the results of this paper have a certain reference value for those cosmetic brands who want to enter the cosmetics industry or enter the market initially in terms of brand strategy formulation and marketing strategy selection.