Because the beer market in Taiwan had been opened up, the monopoly, Taiwan Beer, has been facing intense competition. However, state-owned Taiwan Beer uses flexible strategies to respond to these challenges and always is the leading company in the industry. This study tried to use Game Theory to analyze the competitive strategy of Taiwan Beer in different period of time and find out the relationships between Taiwan Beer and competitor. At the beginning, this research used Game theory to describe the competition in the beer industry. Then, it used Prisoner's Dilemma, the Beach Ice Cream Selling Model, entry-deny strategies, multi-brand strategy and Co-opetition to explain Taiwan Beer¡¦s interaction with others. Finally, this study did not see the competition as the only way that can help companies survive. When the company is thinking about how to defeat others, it also has to be thinking about how to cooperate with others to derive more advantages.