This paper analyzes the impact of the opening of an Intercity EUM (Electric Multiple Units) line, Guangzhou–Zhuhai Intercity Mass Rapid Transit, on GDP and population. By constructing the difference-in-difference (DID) model for whole 24 counties in Zhongshan of China, we found that with the opining of Intercity EMU, GDP growth and population inflow of the counties with Intercity EMU stations are significantly higher than those of without stations. Based on the Sharp Regression Discontinuity (SRD) Approach, we found that with the opining of Intercity EMU, the ratio of Guangzhou's GDP to that of other regions has obviously expanded, thus the opening of Intercity EMU has obviously widened the disparity of regional economic scale.