This article explores the internal and external motivations of company's repurchase decision. In terms of methods, the author uses a combination of theory and empirical research methods and logically uses an analysis process from general rules to special cases to make the conclusions more accurate and have practical meaning. In the research process, the article firstly makes a theoretical analysis, summarizing and expanding various hypotheses about corporate share repurchase motives put forward by predecessors. In addition to analyzing the common signal transmission hypothesis, management incentive hypothesis, and other internal factors, the author also added external factors such as share liquidity and volatility, making the theoretical analysis more comprehensive and innovative. At the same time, to make the research more specific, this article selects Starbucks, a representative company, to analyze its repurchase behavior. In the case analysis, the article at first gives concrete indicators and indexes of each hypothesis based on theoretical research, transforming the qualitative analysis into quantitative research, making the research process clearer and more specific. The article selects Starbucks' financial data from 2009 to 2020 and obtains the corresponding indicator values through integration and calculation. Finally, to increase the conclusions' accuracy, the article selected several main factors through the previous analysis to conduct an empirical test and used Eviews software to perform regression analysis on time series data such as the number of share repurchases and company share prices. The regression results show that a company's number of shares repurchases is negatively correlated with the share price growth rate. The significance level is the highest, proving that the main motivation for corporate share repurchases is to increase the share price. Finally, this article summarizes Starbucks' share repurchase behavior based on relevant analysis results and non-financial information. It provides suggestions for other companies' share repurchase decisions, which have practical value.