This study is a study on the effect of the GTX B route departure station on the price of nearby real estate around Songdo International City, Incheon University Entrance Station, as the GTX B route was confirmed, and 10,142 transaction cases were collected from July 2016 to September 2020 to analyze the effect on the prices of nearby apartments by stage of the GTX B route project according to the preliminary feasibility study and selection through the difference-in-differences method. As a result of the analysis, it was confirmed that the second station influence area was affected before and after the preliminary feasibility study was selected, and it has a significant impact before and after the preliminary feasibility test, but this is not a policy effect, and when the individual characteristics of the apartment are included, the coefficient difference is large, so the robustness is poor. In the preliminary feasibility test, the unit price of apartment transactions is considered to be largely affected by the housing characteristics effect of the apartment and the macroeconomic effect that the entire society is affected. Therefore, this paper analyzes the price changes of surrounding apartments by project stage following the GTX B route promotion, presents future changes in apartment prices near the GTX B route pre-jeong station, and further research should be conducted in accordance with the analysis of various factors such as interest rates and the government’s real estate policy in the future and the promotion of additional projects such as the construction and opening of the GTX B route.