Natural ventilation can effectively reduce indoor pollutant concentrations, including dilution of biological aerosol concentrations. Cross ventilation is one of its main forms. However, in dense cities, the shielding effect between buildings will significantly reduce the ventilation effect. In previous studies, it is rare to discuss the effects of building hollow characteristics on other buildings. As a preliminary study, this article takes two buildings as the research object, and discusses the nine situations of upstream buildings—different window area and position, and their influence on the cross ventilation potential. This article discusses only one direction of incoming flow where the two buildings locates in a line for twice building width. The paper first analyses the reliability of Computational Fluid Dynamics(CFD) simulation based on steady Reynolds-averaged Navier–Stokes(RANS). The results reveal that the reliability of CFD simulation in some cases is insufficient that with a simulation of 20 % porosity it is hard to reproduce the wind pressure on a downstream building by CFD in comparison to 10 % or 5 % porosity. The different simulation reliability may be caused by the instability of airflow between buildings. However, by data from the wind tunnel, we found that the cross ventilation potential of the downstream building decreases with the increase of the window area of the upstream building, which is contrary to general beliefs.