Urban rail transit brings dramatic change to the city's dramatic internal flow changes, which has a great impact on the urban commercial space agglomeration and reconstruction, as the development of urban commercial space depends on the flow. Taking Guangzhou for an example, based on the investigation of the site business circle (500 meters area around subway stations) of agglomeration and the variables related to the metro flow as the breakthrough point, the regularity between the commerce agglomeration and causal factors is analyzed in this paper. Through principal component regression, the relationship between commercial scale and metro liquidity factors such as agglomeration district hinterland market, site traffic, ground bus transfer lines is studied. Finally, the space coupling flow factors and subway commercial agglomeration is further discussed. Based on the above-mentioned, using principal component regression analysis method, it extracts two causal factors on metro stations commercial scale agglomeration, including the market capacity and infrastructure in the influencing factors: the market capacity and infrastructure. The result of building regression method shows that metro stations' hinterland market, traffic and development history (the history of development) determine the market capacity, bringing the quasi-consumers to site business circle. Site' street length, ground transportation and other factors constitute a ground infrastructure factors, providing the material basis for the subway commercial. Both of these two factors together determine the metro commercial scale.