On August 15, 2010, Pre-president Lee Myung Park said “Now, we should prepare a practical plan like a reunification tax for reunification.” And president Park Geun Hye said “The reunification is a jackpot.” Also, according to ‘2014 Mind-set survey about reunification’, the 55.9% of total respondents answered “The reunification be helping to South Korea.” Many Koreans expect reunification of Korea. The reunification is a perennial problem that Korea should solve. If Korea reunify, United Korea will give great effects to the world. So, we should think and prepare about Korea reunification. South Korea has reunification possibility than North Korea. So, I thought 3 subjects on the assumption that South Korea reunify without big problems. The three subjects are positive effects, negative effects and economic structure of United Korea.