We survey the existing analysis methods to horizontal mergers. As the method defining relevant markets, SSNIP (Small but Significant and Non-transitory Increase in Price) test, critical loss analysis, Elzinga-Hogaty test, price correlation analysis, and stationary analysis are introduced. on the other hand, as the method studying economic effect on the horizontal merger, switching analysis, merger simulation, and price-concentration analysis are explained. Additionally, we introduce the new method, LIFO-LOFI market concentration index for exact calculation including actual consumption (export-import ratio). Finally, we examine the effects of horizontal merger between two firms in the Safe Harbor area on the market competition. Using PCAIDS merger simulation, we show that the horizontal merger in safe harbor yields maximum price increases under 5% in most cases.